After the Sugru has cured, remove the watch from the clamp fixture and clean off any excess adhesive.

I've found that running the edge of my fingernail along the seam is a good way to remove the small remainder that may be stuck in there.

It's important to remember that your watch won't have much water resistance with this fix, but that's okay because it wasn't really waterproof to begin with. As long as you don't shower with it on or take it swimming, you should be okay!

If you ever need to open the watch again, you may be in for a bit of an adventure because Sugru is a pretty tough. I would suggest delicately wedging a razor blade in the seam and slowly prying the watch open that way, but I haven't tried this myself.