Do not bother with the button.
Just go into the return, then:
1. Click on Other Tax Situations
3. Under Other Tax Forms
4. Amend a Return, click on the start button.
But be very careful, starting the Amend process will potentially wipe out your old data. It sets the Refund window at the top (green if the IRS owes you money, red if you owe them money) to 0 and proceeds to log the changes from there. These will be reflected in the Refund window, reflecting the impact of your changes on the old filing.
IMPORTANT:
In order to keep a copy of your originally filed form (pre-amending), save a copy of it to some external drive, like a flash drive. Then you will be able to refer back to it if needed. (You will also be able to refer back to the original form if you save .pdf copies of your filing, but that won't allow you to access the data electronically, of course.)
