It's not clear what you mean by "incorporate." Do you mean that you want to transfer information from your 2020 tax return into your 2021 tax return? You can only do that when you first start the new 2021 tax return. If you didn't do it when you started your 2021 tax return, there is no way to do it now without starting over. If there is any information from 2020 that is missing from your nearly complete 2021 tax return, you will have to enter it manually.
