stripped guitar truss-rod nut wont come out?

As a inexpensive beginners bass its really not worth the effort or cost to replace a truss rod, But I really don't follow you as to the plastic, and what you mean by bolt, Nuts and bolts are two different things, If the truss rod is stripped out, as to what I might assume would be what you refer to as bolt, Then just give up and buy a new neck, they're not that expensive and I doubt your capable of removing a fret board, If you mean you got the nut loose and it wont come out of the hole due to the plastic, which alludes me, then yes just remove some of the plastic that's obstructing the nut, then simply replace the nut,

TW, you've got yourself a world of trouble. The truss rod doesn't just slip out. The other end of the rod is firmly embedded in the neck with a stop-plate to fix it in place. Usually, the only way to replace the truss rod is by removing the fretboard.

You have very limited options. One (your Hail-Mary option) is to find a slightly smaller nut in a harder metal....maybe stainless steel... and use it to re-cut the stripped threads. I doubt this will work, but nothing to lose. Next option is to unbolt the neck and hope against hope that the other end of the rod is accessible from that end. I've never seen a truss rod accessible from both ends, but worth looking....since your next option is to replace the neck anyway. Theoretically, you could remove the fretboard and replace the truss rod, but that requires a lot of skill that (no offense intended) you probably don't have. A replacement neck (make sure it's the same scale length) is a do-able option. Good luck.

TommyMc and Nasty are providing you solid answers. The bass is a cheap clone of the classic Fender P-bass, and is below the quality of even a Squier, the import Fender line. This damage might be the reason it was sold used in the first place, and the seller has left town, giggling. Any actual repair will easily cost more than you paid for it. Pass this legacy onto another player, or do a Pete Townsend and smash it on stage, the latter being more honorable. Sorry. Here's, what it's all about:

https://en.wikipedia.org/wiki/Truss_rod