You need to download your DNA test results from Ancestry and upload the data to GEDmatch.com. GEDmatch.com will give you a GEDmatch ID for your kit. (I'm making the assumption that even though you referred to 'gedcom' you meant 'GEDmatch'. On WikiTree, select 'DNA Test Information' from the dropdown under 'Add' at the top of your profile. That will take you to the page where you can enter information about your Ancestry test (including your GEDmatch ID). If I misunderstood your question, please reply with more details. Thanks!