I have been playing this around for half hour, can't get a right feeling.You just visually line it up with the corresponding rubber grommets and then 'gently' push the cover down to seat it. I emphasized 'gently' because if you push to hard you can push the rubber grommet out and it won't be seated correctly and it's easy to lose the grommet. You should be able to sort of feel the pin seat into the grommet as you push down on the cover.
It's a poor design. I suggest not removing the cover routinely and only doing so when there's a real need, which s/b hardly ever.