Report capital gain and loss

I didn't realize I have made gain after loss over £12300 in 2020-2021 tax year, as the stock market was really bad in 2020, I am still in a big loss overrall right now. So I made loss in 2021-2022, 2022-2023. I have filled online form to register for self assessment on 4th OCT, but has yet received my UTN. What should I do now to report those gain and losses?

Hi Flybird2023,
You will need to complete self assessment tax returns, to declare the gains and the losses arising in the tax years  20/21, 21/22 & 22/23.  
You can print of the tax returns at Self Assessment tax return forms.  
If you have a government gateway user ID and password, you can complete the tax returns online for those indate tax years and paper returns for the earlier years.  
You can only do this once you have received your Uniqe Taxpayer Reference number.
Thank you.