If you ordered the CN GMT Master from Joshua? (as you previously stated)... just force a needle (or something sharp) under the rep insert and squeeze it off. It's a rep insert so you don't have to worry about some miniscule scratches, right?
There's no need to remove the whole bezel assembly for that. And when you glue the new insert in remember to turn it a lot in the next 2 hours so the whole bezel ring won't get glued to the case. Don't use too much glue, either (to prevent it).