CGT paid on property sale reported on SA a year early?

I am helping my mum with her Tax Return this year after my father died recently. They sold a flat in late 2023, declared it and paid CGT on it in October 2023. I noticed that she declared it on the 2022/23 SA - which seems like a year too early?! Was that right? If not should I include it on this year's tax return or can we say "it has been declared and paid, it was reported on a Self-Assessment, so we should not report it twice"?

Hi Monty,
As the disposal date was late 2023, this puts the disposal in the tax year 2023 to 2024.
If this is the only gain and it was recorded in the wrong tax year, your mum will need to log into her 2022 to 2023 tax return (do this from the personal tax account) before 31 January 2025, to remove the capital gains section from the tax return.
After this date you will need to submit in writing, an overpayment relief claim (OPR).
Please have a look at the guidance here:
SACM12150 - Overpayment relief: Form of claims
On the format to use with the claim.
All bullet points must be included in your OPR claim.
Thank you.