First up, don't worry. Wait for your notice of assessment—the CRA doesn't want you to change your return until it's been assessed.

If you filed with Better Tax, open that return, make your changes, and review the result. Go to the File section and ReFILE your return using the button of the same name.

If you aren't able to ReFILE you can also use Change my return in your CRA account or even on paper. The CRA's guide to changing your return goes into more detail for when ReFILE doesn't apply.