As the Sharetank owner, you can manage or remove users anytime in the 'Sharetank members' section within Sharetank.
To remove a member:
Open Z App
Tap on Sharetank in the bottom menu
Tap on the three dots (***) in the top-right corner
Tap on the first option in the menu called ‘Sharetank members’.
From here you can review who has access to your Sharetank. If you want to remove someone, tap “Remove” on the right.