If you are not able to utilies the loss in the year it arises, you can carry the loss forward to a future tax year.
You report the loss as arising in 22/23, in your tax return and in the losses and adjustments section, you show what you want to do with the losses.
Have a look at SA108 and the notes
Self Assessment: Capital gains summary (SA108)
The same boxes are shown on the online tax return.