SAM60060 | Interest, penalties and surcharge: interest: amending the effective date of payment (EDP)
From HM Revenue & Customs · Self Assessment Manual
Changes to the effective date of payment (EDP) are made by using function AMEND EFFECTIVE DATE OF PAYMENT, which is available in the Review Interest Officer Processing (RINO) role. This function can be used in most instances to change the EDP. However, where the payment in question is over 12 months old you can only change the EDP by
Transferring the appropriate payment(s) to OAS at Banking Operations
And
Bringing back the payment(s) into SA with the new / correct EDP
In either case interest will be recalculated automatically, the excess being discharged automatically.