Wise or depending on amount in baht you wish to withdraw some banks will allow you to buy baht inside the bank good market value and lower fee not an ATM
If under 30k use atm select "Continue with out conversion" Western Union charges too much for cash pick up and takes off average of 1.50$ from exchange. ( with out thai bank )
If you have someone you trust with thai bank or yourself wise is the next option
If you have the approved DTV once you leave thailand and come back in present your approved DTV and you will then get a 180 day stamp. Once approved you have 5 years to use the DTV.