Hi, I just repaired mine!
You need to take the slide off, which is easy...
Use a knife or similar to unclip it, when off make sure the little black part on the spring is to the front of the slider..
On the cutter mechanism part there are 2 parts of the spring sticking out, they need to go into the slider at an angle so both parts sort of want spring apart...
To put back together you need to extend both parts to the closed position, holding them firmly in place while you click the slider back in!!
You will need patience, I hope I've explained properly and good luck!!