Upside down considering rolling negative equity into lease

According to Edmunds private sale the current appraised value of the Outback is $21,404 and the trade in is $19,450. Since it’s a lease would I be obligated to do the trade-in or I could do a private sale? Right now I can’t get financing through a credit union (or anywhere for that matter) unfortunately. I just cleared up some debts but my score is still so low. Maybe I should wait until my credit heals and then right before I am about to go over the miles (whichever comes first) try to get a loan through a credit union again?

I think I drive about 15 k a year, give or take. So is there any scenario in which leasing again is a good option? I didn’t know what I was doing both times at the dealership. I didn’t negotiate the price or anything so maybe the $540 was just not a good deal? If I do another lease before this one is up how much should I expect to pay more than what someone else pays if they come in and try to get the same car without having any negative equity? I mean, haven’t my high payments of $580 counted towards getting that negative equity down more than $40 a month?

The dealership said now I am 7 k upside down I think. They also said I would need to co-sign if I wanted to do the $540 new lease.

The best scenario would be not to go over the miles though, right? So it is true that if I finish this lease and don’t go over the miles I am done, turn in the current car, and free to negotiate a new lease from scratch? I would finally be rid of the negative equity and everything? Just making sure…

I just don’t know if I can keep it under 10,000 miles until May 2020… yikes