Hi Oscar Palgal,
Foreign capital gains are reported on SA108, so that they can be included in the calculations.
If you paid foreign tax on the gains, then you show the gains in SA106 as well, as this allows you to claim a foreign tax credit relief.
You can claim for losses for the last 4 tax years (19/20 to 22/23).
You would declare this on the capital gains page and elect what to do with the losses, eg carry forward and set against future gains.
For 19/20 & 20/21, it is too late to amend your tax returns, so you will need to submit a losses claim in writing to HM Revenue and Customs Self Assessment BX9 1AS.
There is information on losses at https://www.gov.uk/government/publications/losses-hs227-self-assessment-helpsheet/hs227-losses-2023