If you are using Collavate Business edition, you need to uninstall the app within G Suite Admin Console and your Google apps super admin can uninstall it. Look for a section called "Manage apps" and when you find Collavate look for three dots, click that, and from there you can turn off the application. Click here for detailed guide.
If you are using Collavate Single free/Team edition, Go to Update my profile menu on your right top corner, goes to Terms & Conditions, and click "Remove my account in Collavate" button. Also, you can revoke access: Please refer to this guide about how to remove connected apps.