claiming refund for an old tax period

I filed a self assessment for 2020/21 period but have now discovered there is an error in the submission that means i have paid too much tax. Can i claim the overpayment back, and if so how do i do that?

Hi,
Write to us at:-
Self Assessment,
HM Revenue and Customs,
BX9 1AS,
specifying that you wish to claim 'Overpayment Relief', and detail the change that needs to be made to your return.
We will then amend your return, and the overpayment should be available on your Self Assessment record shortly after.
Thank you.