Which Revision To Use
Use the July 2021 revision of Form 1040-X to amend 2019 and
later tax returns, until a later revision is issued. Use these
instructions with the July 2021 revision of Form 1040-X.
If you are amending a 2018 or earlier tax return, use the prior
revision of this form and instructions both dated January 2020.
All revisions are available at

IRS.gov/Form1040X.

I think you can find your answers in the above.