How can I move a payment from this tax year to last?

Hello Drcat

Is this payment showing from a bank connection in the transactions section of your Self Employed product? If that is the case you can not change the date on the bank transaction. If you want the income to be in the last tax year you would need to exclude the transaction in that section by clicking on the box to the left of the date and if you hover over the symbols there will be an exclude option,

Then it is a case of going to add transaction in the top right and creating the transaction with the date in the previous tax year.