Amending my filed 2020 form isn't working

[wws30]

I've attempted to follow the documented steps to update my 2020 form but got hung up on step #4:  

"Select the return you want to amend, and follow the instructions to make your changes."

There is no ability to select a form to update.  Instead, turbotax asks me to select what I want to update from a completed empty form.  It seems it is expecting my 2020 form to be loaded already but when I tried that there is no ability to "amend a filed form."  Please help.  

BTW, I'm trying to update the amount of covid stimulus I received.  In my submitted and approved 2020 form I overstated the amount of stimulus I received by $1246.  When I update the amount on my original form I see that my refund increases by $1246.   

[LenaH · Accepted solution]

Per the IRS, do not file an amended tax return with the IRS if a mistake was made in calculating the amount of the Recovery Rebate Credit. The IRS will calculate the correct amount of the Recovery Rebate Credit, make the correction to your tax return and continue processing your return. If a correction is needed, there may be a slight delay in processing your return and the IRS will send you a notice explaining any change made.

You only have to amend if you did not claim the Recovery Rebate Credit on your return. 

2020 Recovery Rebate Credit — Topic G: Correcting issues after the 2020 tax return is filed