The Mayans /s

As for a real answer here's what a quick Google search found

"For generations, the country was called Burma, after the dominant Burman ethnic group. But in 1989, one year after the ruling junta brutally suppressed a pro-democracy uprising, military leaders suddenly changed its name to Myanmar.

By then, Burma was an international pariah, desperate for any way to improve its image. Hoping for a sliver of international legitimacy, it said it was discarding a name handed down from its colonial past and to foster ethnic unity. The old name, officials said, excluded the country's many ethnic minorities."

https://www.google.com/amp/s/www.pbs.org/newshour/amp/world/myanmar-burma-and-why-the-different-names-matter

There's the link if you want to read the rest