First, make sure you have joined Heja. You can join using the "Other" category on the signup screen.
Then, reach out to a current coach or admin on the team so that they can do the following and list you under the Coaches tab as well:
Have them click the "Team" tab in the bottom right of the screen
Go to the members tab
Find your name, and click the 3 dots to the right of it
Choose "set as coach" from the menu