We've just added a new bulk tasks so coaches can add members to a group in bulk based on their membership plan.
You can access the new feature from the Admin - Bulk Tasks menu
First select the membership plan you want to apply the new group to. Then select the Group and click the "Start Process" button.
This will do two things
It will add any member/athlete who was signed up to the selected membership plan to the selected group.
It will link the selected group to the membership plan so any future members who signup to the membership plan will also be added to the group.