had a blowout which caused car to roll and roll. how do we go about sueing tire company

Your case could be a products liability case.  What type evidence you have been able to accumulate and gather?  Do you have photos of the scene, the vehicle, is the vehicle still in a pound somewhere, how do you know that it was the tire that seperated, etc... How badly was the person injured? Did they have a seatbelt on? Where were they seated in the vehicle?  What type of vehicle was it?  Make, model and mileage of the vehicle?  How many people were in the vehicle? Is there a police report?  Do you have a copy of the police report?  Or, it may be a Texas Department of Public Safety Crash Report. These cases are not easy to bring, but if you can answer some of these questions, then an attorney can advise you on whether you have a viable cause of action. I would advise you to consult with an attorney who does personal injury cases.