You can extend at immigration you'll need all you did when you applied. Or do a border run or fly to a another country and fly back wich is a few bucks more and way easy !
No need to exit , but you will also have to extend at the office at the 180 day mark well prior truly to get it done on time
The 2nd 90 day report can be done online the extension can not as you will have to show all you showed to be approved to get dtv if you extend IN COUNTRY.
In and out alot never ever has one country muchless thailand stapled a dang thing in my passport.
And you say you have it in front of you but won't shoe as it has some random IO signature on it like that is somehow something that can't be shown or simply blacked out 🤣