I managed to open at ttb Samrong BigC last month. They required the work contract you applied for DTV, Employer Letter translated into Thai, Thai Driving Licence or ID card from your own country (translated into English and notarized), Passport and DTV Visa
They are asking for a recommendation letter from your Employer. Just write a short but detailed explanation of what your duties and responsibilities are. Also the letter should mention that your employer has no objection for you working remotely in another country.