Wheel broke of my Power Chair

I assume you are referring to the caster tire, not the drive tire. You will need to check to see if the rim is a split-rim or a solid rim. A split-rim will have 4 or more bolts holding the two halves of the rim together. If you have flat-free tires i.e., foam-filled solid tires, evidenced by the lack of a valve stem which is used to inflate non-flat-free tires (pneumatic), you would remove the wheel from the caster by rermoving the center bolt acting as the axle. Then remove the bolts holding the rims together. Reposition tire on top of one of the rim halves, then place the other rim half on top so that the bolt holes in the top one line up with the holes in the bottom one. You need to buy a couple of bolts that are about 3/4 in or more longer than the bolts that you removed, as you now must press the two halves back together and the stock bolts probably won't reach through. Put the two longer bolts in opposite of each other in two holes and tighten down. When the rims are pressed together, then put the stock bolts in, remove the two longer ones and replace with stock bolts. Place wheel back on the caster. If you have pneumatic tires (requiring air), make sure to always deflate the tire completely before attempting to loosen the bolts holding the rim-halves together. The same process is used for drive tire replacement. If the rims are not split rims, then it is easiest to buy an entire new wheel and tire as getting it back on is quite a chore requiring a press and lots of tequila! It's easy to break the rims. Good luck.