Myanmarese means “of Myanmar” or “a person from Myanmar.” It is built like Chinese or Japanese: country name + -ese. Though actually almost nobody needs this word. For the people and the language, English already had Burmese, and that is still what most speakers say — you study Burmese, not “Myanmarese.” Many writers just use Myanmar as an adjective too (the Myanmar government, Myanmar food). Myanmarese exists, but it sounds stiff and rare, and some style guides would rather you did not use it. It is not the name of the country; the country is Myanmar (or Burma).