Unscrew the cable at the back of the speedo. Pull out the cable. Wipe with rag dipped in some gas. Dry. You can get cable lube at the parts house, you don't need much. Reinstall cable, when it bottoms out turn it so it slips into the square hole at the bottom gear. Reinstall at speedo end.
If you have to replace it, remember to match the lengths, trimming the bottom.
Not hard at all, luck.