Simple answer - You can't
According to a review posted on Amazon:
Within 48 hours of receiving my printer, and having printed less than 50 sheets, I received a B200 Error. ..........
............I was finally connected to Customer Service. The lady had no technical knowledge but was very helpful ... she phoned the engineering department who told her that the print head had failed. She is sending me a new print head overnight.
There are several other interpretations of the error on various sites but the consensus seems to be that it's not something that you can fix yourself.
If it is still in warranty call up Canon and get them to repair it.