Welcome to WikiTree! The G2G forum is a great place to get answers to questions that you may have.
We do need to stay on topic within the context of the original posted question. Also the 'dna' and 'connection' tags on the original post aren't really conducive to getting your GEDCOM question answered.
So you'll want to post your own separate question about the GEDCOM process, which will allow you to tag your own post with 'GEDCOM', so that folks here that are familiar with that process will see your question and be able to provide help (those folks may not be following the unrelated 'dna' and 'connection' tags that are associated with this post).
Regarding adding your GEDmatch ID to your profile ... if you uploaded your AncestryDNA test results to GEDmatch, you can edit your existing AncestryDNA test info (which you've already added here) to add the associated GEDmatch ID. One way to do so is to use the Add drop-down menu and choose the DNA Test Information option (<== or click here). Then click on the "Edit or Enter More Details" button next to your AncestryDNA test, where you can update information about that test including adding your associated GEDmatch ID. Make sure to click the Save Details" button when you're done.
Hopefully that helps - but if that doesn't answer your GEDmatch ID question, or if you have additional GEDmatch-related questions, you can post a separate question tagging it with the 'dna' and 'gedmatch' tags, so that the appropriate folks will see it.