EDIT: MUST register first - application website below
"Immigration officials can be found on the 2nd floor of Central Festival Samui from 11 am to 4:30 pm from September 21 to 24. Those who want to use the service must first register via a QR code or by contacting Surat Thani Immigration directly on their Facebook page. The mobile service will also be made available in preparation for the end of the "Visa Amnesty" on September 26th."
Website: [members only]/
Facebook: [members only]
APPLICATION: [members only]