Access the payments tab from the Finance & Accounts module and search for the payment you want to transfer.
Click on the payment number and an edit text box will pop up. Here, you can select the correct payee and click on Update.
Once completed, payment will be re-saved with new payee. However, please note that this action can ONLY be performed if the payment is not attached to any invoice. If it already is, the invoice reference will have to be removed first.