their API documentations doesn't seem to have any mention of any API function that allows you to do that. considering this is a very unknown exchange I'd say their API is not used as much so it is not popular and they don't spend time on it.
https://docs.api.ooobtc.com/#2fa0945a-178b-45a1-bd5d-20c7fefd6298you may want to contact their support team and request addition of any feature you think is missing.
just a thought, but I have seen some weird API designs that return your whole balance each time you make a private call. for example when you open an order it also returns a big result containing all your balances. have you checked that?
