Once you have submitted your tax return you would first need to wait and see if your tax return is accepted or rejected. If rejected for some reason you can go back and make the changes and then resubmit your tax return.
If accepted, you should wait until after your tax return has been processed and you have received your refund or your payment has been cleared. You can then Amend the tax return and make the changes.
Here's additional information on Amending:
https://ttlc.intuit.com/replies/3288565