I take it mean they want 6 months bank statements where the closing balance at the end of each month is not less than the equivalent of 500k Baht. They dont care what the currency is as long as, at the end of each statement period, it converts to 500k Baht. Also, it seems that, if there are number transactions in the account you are submitting, they want to see the entire statement - not just the first page. They probably want to see the money flow.