Hi laurensia lay,
We are not able to verify personal details in this forum.
The Self Assessment tax return covers all of your world wide income and capital gains / losses.
If you completed a paper tax return, you can download and print off the supplementary pages at:
Self Assessment tax return forms
If you submitted your tax return online, you will need to log into your personal tax account and amend your tax return.
You will need to go the 'tailor your return' and choose the capital gains option.
Within the capital gains option, you can declare the loss and elect to carry it forward.
You can only claim losses within 4 tax years of the tax year the loss arises.