The phrase "to extend the warranty" means to prolong or lengthen the time period during which the manufacturer or seller is responsible for repairing or replacing a product if it becomes faulty. Full definition
We also have many extended warranties available for purchase. (edmunds.com)
Watch out for extended warranties offered by some dealers. (moneysmart.gov.au)
For example, it offers extended warranty on purchases, price protection, car rental insurance, roadside assistance, travel accident insurance and a cash advance if you lose your card. (creditcards.com)