OP best to contact immigration directly so no hiccups .. below was on internet regarding “”F”
Extension of Stay
Those qualified persons can obtain an additional one year stay permit counting from the date of entry in the Kingdom pertaining to the Office of the Immigration Bureau's regulations on extension of stay. The extension of stay is at the discretion of the Immigration officer. Applicants wishing to stay in the Kingdom longer than 90 days have to file their application at the Office of Immigration Bureau in Bangkok located on Government Center B, Chaengwattana Soi 7, Laksi, Bangkok 10210, Tel 0-2141-9889 (or website at