Under normal circumstances, an approved payment cannot be modified in any way.
However, it is possible to change the tax claim status if there have been a change of circumstances.
To do so:
Navigate to the batch which contains the payment.
On the Payments tab, locate the payment to be modified.
On the far right, click the three dot menu icon.
Click Toggle Tax Claimable.
Select Yes to confirm.
The system will then modify the original payment to either yes or no, depending on the original value.