You can extend your TR visa in Bangkok at Chaengwattana, counter J, if you received a 60-day stamp on arrival. Alternatively, if you arrived visa exempt and were granted 30 days, you should go to IT Square Laksi Plaza, counter K.
Stuart *********
If it’s a TR visa and you got stamped for 60 days on arrival, then you go to Chaengwattana, counter J. If you came visa exempt and got 30 days then you go to IT Square Laksi Plaza Counter K