How do you fix my speedo in my Vw beetle 1968?

Fixing it depends on what the speedometer is doing. Chances are its making a funny noise and the needle is bouncing around. This would be due to a damaged or unlubricated speedometer cable. It is a cable that spins around in a plastic sheath connected to the back or your speedometer and to your transmission. Often times removing it and filling it with graphite powder will solve the problem. If its severely damaged you can replace it with a new one. If the cable isn't the problem you may have to replace the speedometer itself.