If your not sure the name of the microchip facility that supports your cats chip, give the vet a call and see which company they use.
Eat call the company and update the contact info. You might not be able to change the owner info or possibly add your name to it (we have never had that problem) ask them to add you as a second or emergency contact. They should do that with out trouble.
Besides the company name and number you will need the cats chip number from the vet.