The Home Office Guidance was updated at the end of last year to cover multiple applications.

In order to make a new application for pre-settled status, you'll need to show:
  1. Having been here at least one day before the end of 2020; and
  2. No more than 6 months ago, on the day you make the application.

On page 51 of the EUSS Guidance you'll find:

Further applications

An applicant can only have one grant of limited or indefinite leave to enter or remain under the Immigration Rules at any one time. This means that, where a further valid application under the EU Settlement Scheme has been made after an earlier application under it has been decided:
  • if the earlier application resulted in refusal, rejection, withdrawal, treatment as void or in any outcome other than a grant of leave under the scheme, then the latest application must be considered in the normal way
  • if the earlier application resulted in settled status being granted, the further application must be treated as void
  • if the earlier application resulted in pre-settled status being granted, the further application must be considered in the normal way
If you grant settled status where the applicant has pre-settled status, then it will vary (replace) the earlier grant of pre-settled status.

If you grant pre-settled status where the applicant has pre-settled status, then it will vary (replace) the earlier grant of pre-settled status. The date of the first grant of presettled status will remain the start date of their pre-settled status. The expiry date of their pre-settled status will be five years from the date of decision on the further application for pre-settled status.
People with pre-settled status who did not maintain continuity of residence

In order to secure settled status when pre-settled expires, it is necessary to spend at least 6 months out of every 12, in the UK, as noted here: Residence criteria

People who obtained pre-settled status then travelled abroad and ended up spending more than 6 months out of the UK are able to re-apply, as long as they return to the UK before the end of 2020.

They will need to make an application before the end of June, providing evidence of being here before the end of 2020 and no more than 6 months ago when the application is made.

See:Please note that the guidance quoted above reflects this:
If you grant settled status where the applicant has pre-settled status, then it will vary (replace) the earlier grant of pre-settled status.

If you grant pre-settled status where the applicant has pre-settled status, then it will vary (replace) the earlier grant of pre-settled status. The date of the first grant of presettled status will remain the start date of their pre-settled status. The expiry date of their pre-settled status will be five years from the date of decision on the further application for pre-settled status.
Multiple applications

Pages 50-51 deal with general issues regarding multiple/simultaneous applications:

Multiple applications

There may be occasions where an applicant has made more than one application to the scheme at the same time. For example, they may have submitted an online application (with a view to submitting the required proof of identity and nationality by post) but subsequently opted to apply via the ‘EU Exit: ID Document Check’ app (which enables them to provide that proof via the app).

Where this is the case, you must contact the applicant and explain to them that only one application can be made at a time and take the action set out below depending on the particular circumstances:
  • where 2 or more invalid applications are submitted because, for example, the required proof of identity and nationality has not yet been provided, you must give the applicant a reasonable opportunity to provide what is needed to validate one of the applications and to withdraw the other or others:
    • if they validate one application but fail to withdraw the other or others, you must contact them again, inviting them to withdraw the invalid application or applications, giving a deadline of 10 working days, after which (if the applicant has not agreed to withdraw) you must reject any invalid application or applications under rule EU10(1) of Appendix EU - the valid application must be considered in the normal way
    • if for example they provide the required proof of identity and nationality but fail to specify which application they would like it to validate and fail to withdraw the others, you must validate their most recent application (where the other requirements of a valid application are met) and reject the other applications as invalid under rule EU10(1) of Appendix EU
    • if they do not validate any of the applications after being given a reasonable opportunity to do so, you must reject all the applications received as invalid under rule EU10(1) of Appendix EU
  • where 2 or more applications are made, where one is valid and the other or others invalid, and the valid application would result in a grant of settled status, you must grant the valid application and reject the other application or applications as invalid under rule EU10(1) of Appendix EU - however, where the valid application would not result in a grant of settled status, you must contact the applicant inviting them to withdraw the invalid application or applications, giving a deadline of 10 working days, after which (if the applicant has not agreed to withdraw) you must reject any invalid application or applications under rule EU10(1) of Appendix EU and the valid application must be considered in the normal way
  • where 2 or more applications are made, on different days or on the same day, and all are valid but not yet decided, the latest application must be treated as a variation of the earlier application or applications, which must be treated as withdrawn - this is in line with paragraph 34BB(2) of the Immigration Rules, with rule EU10(2) of Appendix EU (which disapplies paragraph 34BB(3) to (5) in respect of applications made under it) and with the published guidance on Applications for leave to remain: validation, variation and withdrawal - you must notify the applicant of this.