Setting Availability:
Log in to Retain → My Availability → Fill in the blanks for the information needed
Log in to Retain → My Availability → Click Add New on the top right → Fill in the blanks for the information needed
Setting Unavailability: (This is not necessary if you have placed your availability)
Log in to Retain → Click Appointments → Calendar → New Appointment on the top right side → click "busy" → set the date and time
Note: If you encounter any issues, contact GTAA immediately.