My mother received 2 T4A(OAS) forms, one for her regular OAS and a second one with $500.00 in block 205. How do I add the second T4A(OAS)?

Box 205 is part of T4A, NOT of T4A (OAS)

Here is how you can enter box 205 on a T4A slip when using TurboTax Online:

1. Click on Find in the top right-hand corner, type "T4A", select "T4A Pension, Retirement, Annuity" from the list, and click go.

2. In the T4A Summary click on "Edit" beside the slip.
3. Scroll down until you reach the COVID Related Benefits section.

4. Enter the amount for "One-time payment for older seniors" (Box 205).

5. Then click on Done with T4A to save your information and again on the next screen Done with T4A Slips.
 

Also, You can simply remove all the amount or change the amount from T4A (OAS) to rectify the mistake

Thank you for choosing TurboTax.