OK so if I am understanding you correctly. Your laptop case/bag zipper was getting caught on the power button, which you didn't know, and finally damaged it.
Well, if the device is still under warranty, I would contact the manufacturer. That would be the best option as they could repair/replace it.
If it isn't under warranty any longer, then you can either try replacing the power button yourself, or take it to a local tech. Also, it may not be the actual button, which is inside, but the exterior button only that is damaged. If that is the case, you may be able to get just a new exterior button.
Now if by some chance the interior button is damaged as well, you will need to replace all of it, and possibly the motherboard.
Again, this is why if it is under warranty, you should contact the manufacturer. Or if you are not comfortable doing the work yourself, get someone who is. Should you choose to do it yourself, I am quite sure there are videos online that can walk you through the actual work.