All you need is :
-a watch with a back you can unscrew ( like in the picture )
-a pair of scissors
-a wire (a pin)
-not a new battery, you don't know the battery number yet, (they are not all the same)
Step 1: Open the bracelet
At the end of the attachment of the bracelet, there are some little holes,
you need to push on the telescopic pin that assembles the 2 parts.
Take your wire and insert it.
Step 2: Unscrew the back
Put your scissors ilke in the picture below. Push hard on it and turn counter clock wise.