Sorry mate, other than pulling it out for a clean out or tapping it with a hammer while trying to disengage it I don't think there's much to do.
The handle has a off centre pin on the end of it that slides the ring gear off of the inner gears but something must be jamming it preventing this action.

Can you remove the clutch lever and check if the pin hasn't snapped off ? Mines held in with a grub screw.