You can find Thai Immigration in Satun on the numbers listed below and on the map. Thai immigration in the province can assist you with your 90 day reporting and also with extending your tourist visa while in the area. They can also extend you retirement visa for you.
If you are leaving Thailand and in need of a re-entry permit then they can also assist you with this as it takes less than an hour to have a re-entry permit issued. You can also speak to them about a residency permit and permanent residency while in Thailand.
If you have a work permit you can also report your 90 day stay to their offices. Note that overstaying your visa is a bad idea and they will charge you 500THB a day and could possibly arrest and deport you if you are caught. The IDC in Bangkok will process and deport you out of Thailand. See the map below for more details.
Thai Immigration in Satun
Burivanit Road, Amphoe Mueang