That’s a shame, I take it the arm is broken right at the end inside.
There is no easy way of taking the front cover off other than reversing the order you put it together. Follow the instructions in reverse order.
It should be just Undoing the side screws, taking off the back, unplugging the dome to take off and then removing the cables attached to the front cover before removing that to enable you to get to the arm mechanism.

Just be careful not to damage any other parts when dismantling him.

Good luck

Mark