After you file

You do not "do" anything to your 2020 tax return because you are waiting for your 2019 amended return to be processed.  You enter your correct information for the 2020 tax year, and let the IRS process your return.  Amended returns are taking 6-7 months to be processed, so that is why you have been waiting.  Mail piled up in trailers during the pandemic.  

You do not say why you needed to amend your 2019 return.  One suggestion----do not be in a hurry to file 2020.  People who are in a hurry to file at the very beginning of the tax season often leave out information that they should have waited to receive--like all their W-2's, 1099's, 1098's, etc. or they make careless mistakes that require them to amend later.  Take the time to prepare your 2020 return completely and correctly the first time around so that you do not find yourself needing to amend it.

Since you filed an amended 2019 return, the 2019 AGI in the IRS system may be a mismatch.  When the 2020 software asks for your 2019 AGI so that you can e-file 2020, use “zero.”  If you cannot e-file by using zero then you will have to print, sign and mail your 2020 return.

Per the IRS website IRS Operations During COVID-19: Mission-critical functions continue:  

IRS operational status and alternatives

Processing Delays for Paper Tax Returns: Taxpayers should file electronically through their tax preparer, tax software provider, or IRS Free File. 

We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.

Do not file a second tax return or contact the IRS about the status of your return.

When the IRS finally opens its mail and begins to process mailed returns you can check the status on the IRS site.

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1