Since you haven't mailed your return in yet, you won't be amending your return because it hasn't been filed yet. To change your return:
- Scroll down to Your tax returns & documents.
- Select 2019 and then select Add a state (you're not actually adding a state, this just gets you back into your return)
- You can now add or change your info.
- Search as needed for things like W-2, mortgage interest, or 1099-B to locate the section you need to revise.
- When you're done, print the updated return and mail it. (Be sure to discard the original return you printed. Only send the updated return to the IRS.)
Note: Instead of mailing it, you might want to e-file your completed return, since e-filing typically means getting your refund faster (22 days or less), compared to filing by mail (4 to 6 weeks).