Player class controls how someone participates on your team, including whether they receive attendance requests, can be invited as a spare, or only receives spectator updates.
Step 1: Open the player
Go to Roster.
Click or tap the player's name.
Step 2: Edit the player
Click or tap Edit.
Find the Class field.
Choose the class you want for this player.
Save the profile.
Not sure which class to choose? See What are the different player classes?.