How to Change the Payment Method of an Expense

Goal:

Head into the Accounts Payable section
Select the Unbilled Items tab below Expense.
Select the [...] button on the far-right hand side of the item you would like to edit.
Select Edit.
Within the pop-up window that appears, select Advanced Change Options at the bottom.
Check the box beside Paying by Credit Card
Select the intended credit card from the drop-down menu.
Select the blue Edit Item button to confirm changes.

Only users with access to Unbilled Expense Items within Accounts Payable will be able to perform the steps listed.
The steps below assume that the approved expense should have been marked as paid by credit card when it had been originally created and approved, rather than reimbursable.