Amendment of last year's return to include SA109?

In submitting my return for the 2021-22 tax year, I think I might need to submit an SA109 for the 2020-21 tax year. If I do, how should I do it? I already submitted this return via the HMRC portal, and cannot amend it to include an SA109. I am using 3rd party software for this year, but did not use that for submitting the previous tax year. How should I make an amendment to the previous year to include an SA109? Many thanks

Is it possible just to send in a manual version of the SA109 since I can't submit it online?

Hi,

You will now need to submit a paper version of the SA109 for the 20/21 tax year.

Thank you.