(IRL) Different helicopters implement force trim in different ways (or some, not at all), and the procedure for using said force trim can be quite different between different helicopters, but, in general...
Helicopters with force trim , when it is enabled, have a magnetic brake that will hold the cyclic in a particular spot. This magnetic brake has a certain amount of spring built into the mechanism such that when it is engaged, you can deflect the cyclic stick to some degree whilst fighting against the springs, but the stick will return to center based on where the mag brake is centered.
To make adjustments to where the brake is holding the stick, you typically press and hold the force trim switch on the cyclic, which disengages the brake. Now you are free to move the stick wherever you want without any resistance. Upon releasing the switch, the brake will re-engage.
Again, each helo is different, but that is the basic principal. Some dont have force trim at all, some have it but rarely use it, and some have it and it is integrated into the autopilot system as well.
For example, my Dad who flew Huey's for 20 years says that force trim (that switch that Fourgrinder mentioned) was never, ever turned on unless flying IFR.
