I used the wrong bolt (too long) for the lower bolt on the side fairing, and tried to remove it today but it feels like the metal insert in the tank is now turning and I cant get the fairing off to get to the oild filler cap.

Help please!!!

Watch out with that as it might also penetrate the tank and make it leak.
Hope you don't blame KTM, your mistake...

Anyhow, use a cordless drill with the correct size allen key socket or cut an allen key down so it fits in the chuck.
put the cordless clutch on half so you get the rattle effect, make sure the drill is set to anti clockwise and I guess high speed works the best.
put the key in the bolt and pull it slightly sideways (on the piss, you know what I mean) this seizes the insert in the tank plastic and give it a burst.
Don't overdo it or it will ruin it!
if you get it out glue the insert solid with some superglue carefully applied on the outside of the insert. don't put the bolt in till all is dry properly or you could glue the bolt in the insert.
Good luck!