Can anyone please give or have any advice for me how to go about the least stressful way of getting a 12 month visa , thankyou

American on visa exemption. I'm having issues understanding what a local Muay Thai gym in Ayutthaya needs from me in order to start studying. I can only understand via translated phone call with gym owner so far, afraid information being lost in translation. What I gather is the gym is saying I need a paper from my embassy saying I can study here or something. Im not sure what hes talking about. I thoight i need a form from the gym to take to the local immigration office. Any helpful advice appreciated. Thank you in advance.