Very easy to do as I did it on my nikko 3yrs ago.
Put a target out to 10yrds,unlock the locking collar on the objective lens, you can do this by screwing the sunshade on to get more leverage. Lock it in place by wrapping gaffer tape on the area where it screws onto the scope.
Now put some more onto the other side of the scope body and put a cable tie around it,put it on in the direction so it tightens as you unscrew it,anticlockwise.
I can't rememder which way it needs to be turned,the objective lens.You may need to shape a piece of metal to fit into the adjacent grooves on the locking collar to enable you to turn it in or out.
Put it on full mag and focus on the ten yrd target.
Now slowly screw the lens in or out untill in just starts to get blurred at the 10yrd target.
If you have a close focus adapter you could parallax it to say 12yrds.You will then get slightly bigger gaps between 50-55yrds as the parallax works on a liner scale.