Thanks for helping to build our tree here and for adding your DNA test info to your profile.
There are multiple ways to get to the screen to edit your DNA test info. You can click on the Add drop-down menu and choose the "DNA Test Information" option (<== or click here). Scroll down to your FTDNA autosomal test and click the "Edit or enter more details" button next to it. In the GEDmatch ID box, correct your GEDmatch ID, and then click the Save Details button.
Let us know if you still have questions.