I can recommend Thai Immigration services. Over 70 offices throughout Thailand. Any visa or extension from between 1900 to 2000 {excluding elite} Down side? Some inconsistencies between offices, have to do your own photocopying.
I think it just says to do your 90 day report. Like it says on my extension. I know of some people on this extension that did bother to read their stamps and asked immigration (not Kpng) how to do this and were told don't bother.
This is to do with this new poster that got put up there. Maybe someone can get a picture of it so we can get the correct context. Also, I understand tvar people are complaining that they weren't told or warned about this. Is it not written in their passports {bottom of the Covid extension stamp}??
As far as I'm aware, it has been possible once you leave Quarantine (with all your paperwork in order) to travel directly to Samui. That said, I understand Buses to the south have been cancelled and you may want to check if flights are still going to Samui (or Surathani). Best of luck
Try heading to your local hospital and asking them. They might be able to slide you in as sometimes thet have no shows or people unable to have it due to high blood pressure and the like. If tyou have a wp that might help or Thai speaking friend.