You arrived visa exempt 30 days? You go to immigration for 30 day extension 1900 baht. Need passport size photo, copies of passport main page and stamped page, your departure card, fill out some paperwork..
I believe they can ask for medical and police clearance but not always necessary probably depends on the immigration office. May want to check with them in case it's not required.
you extended a visa exempt for 2 months? The only 2 month extension I know of available currently is Covid extension but you must have 30 day extension first and at present are available until March 25th (word is this will likely not be extended as borders open up) It is at the discretion of immigration office and the cost is 1900 baht.
Yes it's 30 day extension costs1900 baht and involves a little paperwork, copies of the main page of passport, entry stamp and your departure card, 4 x 6 cm photo and visit to immigration office.