The throwout bearing is a light press fit over the collar. Easily removed using a "pusher" such as a large socket, chunk of pvc pipe, etc.
If you mean "how to remove collar/bearing assembly from the cross shaft"...
In this pic of a t18 setup for a Scout 800 with the pancake bell housing, ya can see the cross shaft and release fork. Behind the mounting point of the fork to the shaft there is a set screw that needs to be released.
Then the shaft is driven out of the bell housing after cleaning as much shit from the shaft as ya can so it can slide through the various holes. There is also a "key" inna keyway machined into the shaft that locates the fork to the shaft. That will be stuck with grunge also.
If ya don't wanna remove the cross shaft, then simply pull the tranny from the bell housing and slide back to remove the throwout bearing assembly.