It’s fairly easy once you get the knack, I’ve done a few recently mostly due to being sited in “lively” households but also due to wires breaking at the pivot point.
Push a 2.5mm allen key, or smaller, through the side access slot whilst keeping slight pressure on the cover, pulling up and out gently, it will release. DO the same on the other side and it will pop out. It does take a little practise and confidence.
Remove seatbelt fixings and with the arm folded down you look down into the center of where the arm pivots you will see a nipple the needs to be pushed in to release the top cover.
There are a couple of different designs, one of which I had to undo the arm pivot bolts to remove the bottom cover
I went to a job the other day and got the third degree from the user – turns out they’d kicked out one guy who was just attacking the cover with a screwdriver, he was trying to just lever it apart along its length.