Finally...
The best route to get your manuscript back from PA is to inform them that you will no longer be buying or promoting your book anymore. Keep it polite and professional and ask to have your rights returned.
Once this happens, you can then shop the trilogy around, but series are hard sells.
something I am an expert on.
Rewrite the second book to stand alone. Retitle it to some name not associated with the first book.
Make the third book the second book.
Write a third book that completes the series.
The first hurdle you will have to jump with any publisher is to have a viable book. The new first book must be marketable, polished to a brilliant shine, and so engrossing that agents and publishers will drool over it.
The second hurdle is the ugly elephant sitting in the corner. They are going to google you and there will be the PA book. When they ask, confess, admit it was a mistake, and move on.
A good book trumps all.
My trilogy was about a character set that I created to run for many books. I had a repeat clause with PA and lost two books. I wrote the third with abandoning the first two in mind.
I later got my rights back and my publisher agreed to release them as an anthology.
It is possible to save the trilogy, but it far more work than just letting it go and write a new, better book that will WOW the publishing world.
If I had to do it over again, I would have just taken my loss on the first book, sent PA a crapfest James Frey type biography, and moved on to better things.