TalentLMS is a website that users can visit using their browser. The behavior to lock the page or screen during the test requires control over the end-users devices, which is something that cannot be affected by TalentLMS.
Therefore, what you can do is add a timer on tests, so that learners do not have the luxury of searching for answers to the test questions. You could also prevent copying questions' text, to make searching for the answer even more time-consuming. Here's how: How to prevent users from copying the question text.