Hello, dear tester!

You can accept the invitation, review the test, ask TL about your doubts in the chat and in case you accepted a test and want to quit it later on, you will find this option at the bottom of the right sidebar on the test overview page. The quit option is only available as long as you haven't submitted bug reports and completed other tasks such as Paid Activity Sessions, Reproductions or User Stories in the test and the test is not over yet. Here's an image of the Quit test button.