Update: we stripped the clutch back off and took apart the star gear we were actually able to manually rotate the drum and get it to go through all the gears, it extremely stiff hopefully from sitting dry for so long rather than bent forks.
Our plan at the moment is to soak the drum as best we can in oil, reassemble and fill up oil and run the bike (in neutral) to get the oil round all the internals and get some heat into it, hopefully that will ease the seize and rectify the issue.
Otherwise it’ll be a full strip down and see whats going on with the internal if we have no success in freeing the drum up for normal operation