Here's the info for bangkok (so once you get back IN the system you can use the mail in method if you need to)
you need, 90 day report receipt, copies of the data page of your passport, your current extension, your most recent entry stamp, your TM6 departure card and a filled out TM47 - 90 day report form.
You enclose a self addressed stamped envelope in the packet and they mail your 90 day reporting receipt back to you. Keep in mind not every office allows mail in reporting
Here's the address:
ATTENTION 90 Day Reporting
Immigration Office Division 1
Chalermprakiat Government Complex
120 Moo 3 Chaengwattana Road Soi 7
Thungsonghong, Laksi Bangkok
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