Once you have made your SLfT return you can make an amended SLfT return within 12 months of the filing date for that return. The filing dates for each quarterly period are outlined in SLfT5002. If you make the return later than 12 months after the filing date then no amendment is possible.
Separate guidance is available on How to amend an SLfT return.
You must pay any additional tax due as the result of the amendment at the same time as you make the amended SLfT return – see SLfT5004.
If as a result of the amendment you are due a repayment of tax, but you have failed to make a previous SLfT return that was required, then we do not have to make the repayment until you make the outstanding return and pay any associated tax.
If the amended return contains an inaccuracy, you may be liable to a penalty – see RSTP3011.