Mr Paul is right, there should be a split in the collet for adjusting AND because they are held on partially by the spring pressure of the slightly smaller sized collet/shaft relationship.
Once again, photos are important in helping us to help you. The more info you can provide, photographically, serial number, model type etc, the better:-)
This could have been a modified repair job?
Back to your original question, I don’t think that you want to attempt a re-collecting the hairspring job Haha
So what you can do is….
1. Remove the balance wheel
2. Looking from the roller table side up, get your finest tiniest screwdriver and GENTLY insert it between the bottom of the collet and the balance arms.
3. Once part of the screwdriver tip is inserted, GENTLY twist the screwdriver to try and lift the collet off the staff.
You have to do this in two or three different positions and a few times, if it’s tight you don’t want to break anything or take it off crooked.
Again this takes a certain gentle skill, you can easily slip and FU the hairspring.
Once you have the hairspring removed, replace the balance in the watch, WITHOUT the cock.
Center your pallet fork, set the roller jewel center between the forks.
Visually superimpose the position of the HS stud in relation to the cock.
Make a note of the position of the hairspring/balance.
Press the HS back in place using your staking set.
