This is on your Berg?
I have a few KTM axle equipped bikes and the axles can get gummed up with crap. I clean mine off with acetone or similar and wipe it spotless. Then I very lightly lube it with some grease like Belray waterproof.
Make sure you wheel spacers and bearings are clean too as they can create drag. I go in from the brake side, so you need to get the caliper bracket in. Then I make sure the brake pads are clearing the rotor by splaying them out with my fingers and gently tap the axle through the first spacer and into the hub itself. Now I line up the axle hole with the swingarm and gently tap it in with a deadblow hammer. Toss on the axle adjust spacer and you should be good.
Once you get one side started it should be a matter of getting the other side close and the axle should pull it into alignment until you jimmy the wheel to clear through the swingarm. I guess I've never had an issue other than the axle being gummed up with dirt/grease.
We're not out here to rough it. We're here to smooth it. Things are rough enough in town.