IAS 8.42 allows prior period errors to be corrected retrospectively. So if you consider that non-writing off of your debtors in the previous period as an error, then you can credit the debtor and debit the accumulated profit instead of the current P&L.
Generally changes in debtor provisions/bad debts come under changes in accounting estimates which should be corrected retrospectively. However if you consider that you did not write off in the previous period although you had the information of debtor going bankrupt or something similar but the write-off was not done by mistake, then you can say that it is a correction of a prior period error.