This TurboTax Canada FAQ tells you how you can do that using ReFile: I've filed my tax return. Can I still make changes?

To enter your T4A(P) Statement of Canada Pension Plan Benefits in TurboTax Online, search for “T4A” on the Tax Home page (2024 tax return on the left), and select “T4A(P)” from the list. You can also find the T4A(OAS) Statement of Old Age Security in the same way.