If your solar powered watch has stopped working please pull out the crown/winder on the side to the first or second position, as applicable, and leave it under a light source for 24 hours as the watch may have completely depleted its charge.
There are many kinds of light you can charge your watch with but some work better than others such as sunlight or UV light.
After charging you may need to reset the home reference positions, to do this look inside your watches instruction manual under home reference / zero positions / calibration which is generally located towards the end. Please note this does not apply to all watches but is very common with radio controlled, analog/digital hybrid and bluetooth watches.