I am assuming they are both clipped together (with very strong clips) like all other Costar boards. In this case you should look for advice on how to open a Filco (I am too lazy to find it for you right now, its somewhere on the forum..).
When first opening it, you will feel like breaking the board because the resistance is so high. In the end I have always opened all my Filco boards and they never did break, but yeah it has a scary feeling to it.