How to move a watch from right wrist to left wrist?

Hi, welcome to the forum! Changing the category isn't going to change where the mesh is positioned. You have to export the mesh, open it in blender and manually edit it so that it's on the other side. Then you'll have to apply the weight for the other wrist.

Here's a GUIDE that can help you out. From step 13, the image below will show you where the weight is. You can double click the name of the bone and change the letter from L to R and then click "assign" to apply the change on all the mesh.

As for the manual editing, i suggest seeing any beginner tutorial for blender to learn the basic tools. Here's a video for rotating and moving stuff around. i HIGHLY suggest using the numbpad on your keyboard to work with a fixed camera angle. 1 will change to front view, and 7 to top view. Holding CTRL while moving or rotating will give you fixed positions to keep the right angles.



If you consider this too difficult or you're not sure if you want to go through with it, please let me know and i can move your thread to the "requests" section.