1. First you have to leave Thailand and apply for a Non-O single entry visa at the nearest consulate or embassy. You can show your own bank from your country.
2. Once you get your visa, re-enter Thailand and open a bank account immediately. Say the reason is for a Retirement Visa. Prepare your Resident Certificate and your own Sim Card to open a bank account. This is easy at this point. Then put 800,000 baht in it.
3. Go to Immigration about 1 month before your current visa expires and apply for a Retirement Visa extension. Job Done!!!
VISA and Mastercard are useless at ATMs in Myanmar. But if you have JCB and UPI it's fine. For dollars, there are some people selling dollars around the embassy. Try negotiating with them. I think you have to pay a bit more. Or try asking people who are on the same visa as you for help. They often have extra dollars. May you be fine.