Go to Kershaw directly. Its Limited Lifetime Warranty covers the original owner against defects in materials and construction, is non-transferable, and excludes normal wear, rust, improper use or maintenance, accidents, loss and theft. Kershaw's warranty page carries the current process.
Because Kershaw's warranty is explicitly non-transferable, being able to show you are the original owner matters more here than with brands that cover the knife rather than the person.
Keep your order confirmation. On a Kershaw it is doing real work.
Describe what failed and how the knife was being used. Kershaw excludes improper use and maintenance, so an accurate account of ordinary use is what distinguishes a defect claim from a wear claim.
Rust is an explicit exclusion, so a corroded blade is unlikely to be covered regardless of how it happened.
Read the current warranty page, linked below, and follow whatever process it sets out. Posting a knife without following it is the most common reason a claim stalls.
Warranty terms are set by the manufacturer and can change. The maker's own warranty page, linked below, is the authority. We repeat what it says; we do not extend it, and a retailer cannot promise coverage a manufacturer has not offered.