You have two options... you can move it in two steps when you are in the 400k months... move 400k to the new account and keep 400k in the old for at least one more day before you move it. You need to show bank statements from both banks for your next extension. Or... but that depends on your local immigration... you can move the 800k in one step if it appears the same day in the other account. As said... you have to ask your immigration first, if they'll accept it...
Nah... I highly doubt that it was that easy... Phuket isn't a good place for opening accounts anymore, not without the requested kind of visa. He might have been lucky using an agent... but actually the most agents don't offer this "special" service anymore... 🤔🙄