Option A — from the manager's profile:

1. Open the manager under Customers and go to the Members tab.
2. Click Add Member (or Add First Member).
3. In the Add Member dialog choose the User (search box; only customers who are not already someone's member are listed).
4. Set the Subscription Settings switches and click Save.

Option B — from the member's profile:

1. Open the member under Customers, Members tab.
2. In Account Manager, search and pick the manager (or No account manager to unlink).
3. Adjust the Subscription Settings switches that appear and click the page's main Save.

Either way the member immediately appears on the manager's Members page in the customer dashboard.