To cancel a Vehicle Registration Certificate (RC) in Bihar, you need to inform the Regional Transport Office (RTO) where your vehicle is registered, typically by submitting an application along with necessary documents like the original RC, insurance certificate, and a police clearance certificate, if required. You may also need to provide an affidavit confirming the vehicle has been scrapped or is no longer in use. The RTO will verify the documents and initiate the cancellation process.