How do you replace or repair a laptop button, my b button is broke.?

Answer:

The buttons should merely pop right off. You can be in motion to a used/repair shop and see if they have a another one or instruct one from the manufacturer. If the B mechinism is broken, lone a professional repair will work.

Added:

Look carefully at the pay for of the button and make sure no pieces are broken or bent over to prevent it from slipping fund on. Look at the keyboard and be paid sure nothing is bent. The buttons are designed to pop rotten and on.
What kind of laptop? What button? One of the upright keys or the power button or?