What can one do if they are in the US on a O2 visa but is currently out of status?

Not enough information.

How long have they been out of status? If less than 180 days, best to leave the US as that marks the 3 year bar date under section 212(a)(9)(B). O-2 is for someone accompanying an O-1, if not married then marriage to a USC will allow for AOS here in the US under section 245(a).

I recommend you consult with an experienced immigration attorney. Good luck.