To apply for a Covid Extension in Thailand, you typically need the following documents: your passport (including copies of the data page, most recent visa, recent stamp, and departure card), a TM30 form filed at the immigration office, appropriate forms specific to your immigration office, a letter from your embassy stating you cannot return (or a printout indicating they do not issue such letters), two passport-sized photographs, and a fee of 1,900 THB. Additional requirements may vary between different immigration offices, including potential requests for the ID card of your property owner and copies of all stamped pages in your passport.