If you are a driver, some passenger made a safety complaint against you. It is probably a total fabrication designed for nothing more than to get a free ride. College kids, in particular, like to pull that just because they can.
I could give you the Uber Support phone number, but they won't help you. You will have to deal with the safety team.
The safety team will not give you much information, and definitely will not tell you which ride caused the complaint, so if it's a non-specific complaint you most likely will not be able to figure out what caused it. It will take 3-4 days to a week for the safety team to resolve the "complaint," and then you'll be reinstated.