Ensure you’re signed-in to the Google Account with the email address matching where you receive shift request invitations and click the Edit your response link
Instructional videos
Initial setup
How to initially setup Google Calendar invitation settings so that you can view shift requests at https://calendar.google.com
Individual shift requests
How to respond a one-off shift request
Shift sign-up
How to sign-up for a shift
Regular (recurring) shifts
How to accept a recurring, e.g., weekly or fortnightly, shift request
How to decline an individual shift when you have a regular recurring shift