This guide will explain how to edit the affiliation of a member. The affiliation are always attached to the PTSO membership
1. On the athlete profile details, open their provincial/territory membership
2. On the Membership Details, scroll down to the Membership & Other Affiliates section and click on Edit 
4. The new affiliation will then be added to their affiliation
If both affiliations are still accurate you can keep both of them. Otherwise, you can click on the garbage icon next to the old one.