Look up videos on Youtube by this guy:
yusuf benallal
https://www.youtube.com/@RideWithYusufb
He's in car sales and provides a lot of insight on how you can work deals when there are less than optimal situations. One thing I never thought of that he's proposed to make something work is to use new car incentives on leasing to absorb any negative equity on a car being traded in. He's upfront and honest with the callers he takes whether he can help, provide alternative car options from what they were originally considering, or that it's better for them to hunker down and pay down their current car. He also provides one on one consulting to give advice or negotiate car deals on your behalf.
As to selling your car yourself, it's not going to happen without you being able to pay off the negative equity plus the proceeds from the sale to get title in hand.