Right, you are not going to like this . . . .
Reading your other posts it seems your garage are somewhat clueless and I suspect they have made a blunder with your Transfer Box (TB) while it was out.
I'll dig out some pictures . . .
At the rear of the TB, top side, there are two plugs with Hex sockets in them. Inside here are a pair of springs (nested - the small one is inside the larger one) and a 'detent ball'
These click into notches on the rear of the selector shafts to provide a positive registration when the various positions are selected.
Worse - in between the two shafts is an 'Interlock Plunger' that prevents the shafts from selecting the wrong combinations of functions. I.E. you can't select 'Low' with the centre diff unlocked . . . .
What I think has happened (I've done it myself) is that someone has pulled the right-hand shaft too far forward and the detent ball has jumped in behind it - jamming the shaft.
This is easy to do on an Auto TB as the selector shafts stick out of the front, on a Manual they are inside (where you have a blanking plate).
This is the arrangement inside . . .
This is what the ends of the shafts look like (you don't have to strip the rear cover, speedometer drive or Companion flange):
The 'fix' is to:
1. Remove the TB.
2. unscrew the two detent plugs and tip out the contents - as above (you may have to move the right-hand selector shaft forward a bit).
3. With the RH shaft pulled forward, re-insert the interlock plunger:
4. With the TB tilted to the left, move the RH selector shaft back and re-fit the Detent balls, springs and plugs to both sides (this can be fiddly).
5. Check that all functions work - without pulling the RH shaft too far forward, or you will be back to 'Step 2'

.
6. CAREFULLY re-install the TB and check it over.
7. Warning - the TBs weigh 50 Kilos so not an easy lift from underneath whilst lying on your back (DAMHIK).
Good luck, let us know what you find.
Bob.