I thought I might add a few images to this post. If the rollers on your 91/G3/93 are stuck out and you're not sure what to do, see if the images below might help.
If you already have the bolt/carrier apart start at step 4.
Rollers Stuck Out
(1) As you look at the bolt face, holding the bolt carrier, turn the bolt 90 degrees in a counter clockwise direction. It can be tough to do, there's not a lot of room to grab onto.
(2) Now slide the bolt forward about 3/16", You don't want to slide the bolt off the locking lever.
If you slide the bolt off the locking lever, continue onto step 4.1
(3) Now rotate the bolt 90 degrees clockwise.
The rollers should be loose and you should be able to easily slide the bolt/bolt carrier back in the rifle.
If the rollers didn't quite go in all the way, push the bolt away from the bolt carrier.
(4) Insert locking piece/firing pin & spring
(4.1) Turn until the flat of the locking piece is parallel with the edge of the locking lever, you should be able to see the catch of the locking piece in the 'window' of the bolt carrier.
Now push the bolt, A ,all the way back to the carrier.
If it is difficult, simultaneously push on the end of the locking lever, B
Now rotate the bolt about 45 degrees CW.
Now continue with Step (2) above