On most production folders this is a manufacturer job rather than a home repair, and on several brands disassembly voids the warranty outright. If the action has gone gritty, clean and lubricate first: worn washers are much rarer than dirty ones, and the symptoms look identical.
Gritty action is nearly always contamination. Flush the pivot with warm soapy water, dry it thoroughly, oil it, and cycle the blade. That fixes the large majority of cases.
See fixing a knife that will not open smoothly before you reach for a driver.
CIVIVI, for example, voids its warranty on third-party repair or modification. Other makers take a similar line. Taking a knife apart to inspect a washer can cost you coverage you would otherwise have used.
Read the maker's warranty terms before disassembly, not after.
Photograph every stage, keep the parts in order, and expect to need thread locker on reassembly. Washer material matters: phosphor bronze, PTFE and nylon behave differently and are not freely interchangeable.
See pivot washers for what each material does.