You can amend your tax returns for 2 years from the end of the 31 January deadline for the tax return, eg. deadline for 21/22 return is 31 January 2022, so it can be amended up to 31 January 2024.
You can claim foreign tax credit relief by amending your tax returns for 21/22 & 22/23.
For 19/20 & 20/21, you will need to make an overpayment relief claim.
For 19/20, you will have until 5 April 2024 to make your overpayment relief claim in writing.
If you make it after this date, it will be too late. It is currently too late to make an overpayemt relief claim for 18/19 or any earlier tax year.
All overpayment relief claims should be sent to H.M. Revenue and Customs Self Assessment BX9 1AS.
The guidance at SACM12150, asvises of the claim format that is required:
SACM12150 - Overpayment relief: Form of claims