What you are experiencing can sometimes happen if your neck has gone through some shrinkage due to environmental conditions. It is a simple process to replace the tuner.
1. Remove the peg from the hole.
2. Cut a small round circle out of white paper.
3. Put a small drop of super glue on the tip of the tuner where you see the splines (those little ridges around the end of the tuner that goes into the hole).
4. Put the small circle of white paper around the splines so that the drop of glue will hold it in place as well.
5. Now place the tuner back in the hold being careful to align it as it was originally.
6. Hold the tuner in place for a few seconds while the glue sets.
7. You can GENTLY tap it with a RUBBER mallet if you want to set it in place.
8. It will now hold. The piece of paper is there to fill in the gap that has occurred through neck shrinkage.
Let me know if you have any further questions on this. You can call me at our toll free number, 800-845-7791