Each task in your teststar account has a time limit shown in its description. Once this time expires, your progress will no longer be tracked. You can then remove the task by opening it, scrolling to the very bottom of the screen, and clicking "Abort this task" under the goal table.
⚠️ Please note that this action cannot be undone. If you cancel a task before it expires, you will permanently lose the chance to earn any remaining rewards in this particular task. Make sure you definitely want to end the task before confirming.