I removed all of the adherent paper, washed the emulsion side with warm water rubbing gently with a finger to remove the developer grease, then washed off the black layer on the back with clorine bleach using rubber gloves, and rinsed the neg carefully.
I really have no clue how Pola/Instax peelapart work. There is also missing 1 cm because my scanner only can screen max. 7 cm hight.
The neg is rather dark, can it be that there is a lot of silver in the emulsion? I still have some bleach from c-41 color development, I bleached and fixed and neg became much brighter, now waiting to dry.
Here's the positive and the unbleached inverted neg: