You CAN decock one quite easily with a tiny amount of practice.
FIRST- ensure the weapon is clear! Other wise the firing pin will be resting hard on the primer of a loaded round...
Just raise the knuckle until it comes to a sort of pause (the effort to continue will become greater at this point), and then pull the trigger. The whole toggle assembly will close- you don't have to hold on or anything.
The linkage is pivoted upwards roughly 30 degrees at the decock pointif I remember correctly, but it's not critical. All you are doing is taking the tension off the striker spring and bringing the f.p. to it's full fwd position.