There are just a few simple steps for granting someone room admin access.
Navigate to the room you need to grant access to
Click on the ellipsis next to the Join Room button, then click on "Edit Room":
Click on the "Assign Access" tab:
Click on "Edit Admins" at the bottom of the edit box:
Search for the person you want to give access and check the box next to their name:
Close the box and click "Save Room"
Let the user know that they should refresh their screen and they will then see the ellipsis next to the "Join Room" button on the room they have been given admin access. When they enter the room they should also see the edit button at the top of their screen.