Click on your avatar in the top right of your gmail or chrome browser and select ‘manage your google account’.

Then select Data and privacy from the left hand menu

Scroll down to 'data from apps and services that you use', then select 'third-party apps and services'.

Scroll down the list and select Surfboard. You'll then be taken to a page with details about the access Surfboard has. Select 'see details'

Now, click 'remove access'. Surfboard will then be disconnected from your Google Calendar and your schedule will no longer sync.