If you entered on an actual tourist visa which you applied for and got before you travelled to Thailand and were stamped in for 60 days, you will go to the Chaengwattna office Immigration office, Government Complex Building B.
You will go here.
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And you can book online
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If you enter on a 60-day stamp for free, it is NOT a tourist visa, it is a visa-exempt entry if you are eligible to apply for a 30-day tourism extension.
You are going to go to the IT Square Laksi Plaza temporary office, just next to Lak Si station of SRT Dark Red Line / MRT Pink Line.
You will go here.
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