Selected seats stay highlited for too long. When the page is closed browser remembers selected tickets.

Good morning.I have a problem. When a customer is selecting seats from the venue, doesn't finish the transaction and logs out or closes the browser, the seats that he selected are remembered. Therefore they are blocked from booking for other people. How to set it to expire after logging out or reloading the page? I want to avoid the situation, when somebody selects few seats, closes the page and doesn't make a booking and also can't book these seats, because they are selected by someone else. Please help me, because I don't know how to resolve this problem.