There's a book on this very thing available at the Public Library that's directed towards 'Case' pocket knives, but the information is valid for all.
The Complete Book of Pocketknife Repair: A Cutlers Manual Paperback – March, 1995 - Ben Kelley Jr.
It's 'not' easy, and guys who can do this are few and far between - and are quite proud of their abilities when they price out their work.
In many cases, their prices supersede the value of the knife...
Scouts Out!