What is the process for extending a 30-day visa in Thailand after crossing from Cambodia?

If you've entered Thailand from Cambodia on a British passport and received a 30-day visa, you can extend your stay by applying for a 30-day tourism extension. You must visit the immigration office that corresponds with your address. If you're located in Bangkok, go to the IT Square Laksi Plaza temporary office, conveniently located next to Lak Si station on the SRT Dark Red Line. It’s advisable to book an appointment online before visiting.