Go to My Hub > My Roster. It has two tabs, Competitors and Coaches. Click Add and enter:

• First and last name, exactly as they are registered with your sanctioning organization.
• Gender - this must match the levels you will enter them in. Getting it wrong is the single most common reason an athlete cannot be registered.
• Date of birth - used for age-based levels.
• Organization number and level for each organization you compete under.

Someone who both competes and coaches goes on both tabs, using the same membership number. It is one membership with the organization, so both entries legitimately carry the same number. Adding the same person twice in the same role is still refused as a duplicate.

You only do this once. The roster carries forward from event to event and season to season.