You can choose to leave a project at any time. If you choose to leave a project it will no longer be available in your 'Projects' list, but the work you have done in the project will remain as is.
To leave a project you can do the following steps:
Log in to web.checkd.it and navigate to the 'Projects' section in the menu on your left-hand side.
Open the project you have in mind and go to the 'People' tab.
Click on the 3-dot icon beside your name on your right-hand side.
Click on 'Leave project' and a new window will appear with a warning.
Click on 'Leave' to leave the project.
See the screenshot examples below:
Click here if you wish to learn more about how you can remove other people from a project.