PREVIOUS YEARS SA 800 2020/2021

I didn't complete a tax return for 2020/2021 and need to find an form to download as HMRC didn't enclosed the relevant forms, anyone suggest anything or have a link to the correct form? Can I download one of the others and change the date on the form?

Hi
If you’re sending an SA100 tax return for the 2022 to 2023 tax year or earlier, you are able to get forms from the National Archives.How to complete your tax return for Self Assessment 
As the Self Assessment deadline for these tax years has passed, we advise that you send your tax return or payment as soon as possible. You will also have to pay a penalty:
Self Assessment tax returns