Enabling / Disabling scheduling for a specific user is easy.
FROM THE WEB APP
Step 1: Go to Settings > Users
Step 2: Click the "This user can be scheduled..." box.
Step 3: Have your team member edit their scheduling availability.
Step 5: Done
NOTE: Scheduleable cost add $40/month per user on the "Professional Plan". Additional, Non-Scheduleable users are free on the "Professional Plan".
FROM THE MOBILE APP
This setting can only be changed by logging into the Web App at this time.