Use a spudger to pry the back cover of the watch off by placing it under the seam of the back case.

The back cover is glued on and may be difficult to remove. It might help to heat the back cover before prying in order to soften the glue. If doing so, be careful to not burn yourself.

This step requires a good bit of force to pry or apply heat back cover off because the back cover is glued. Be careful not to the break cover from too much force.