REPAIRING DAMAGED OR LOOSE TILES
A damaged or broken tile should be removed and replaced by a good tile mechanic only. If the tile is simply loose, you should be able to repair it yourself. Just clean the back and sides of the tile of all grout and bonding material. Apply fresh mastic and set the tile into place. Let dry for 24 hours, then grout. If you have more than a few loose tiles, it's best to consult a professional tile mechanic to handle the job.
Some final words about maintaining ceramic tile ….
When you boil down all the facts, maintaining ceramic tile is simple. Most issues can be eliminated with a few preventative measures. Once the tile is in, you can enjoy years of functional benefits and visual enjoyment.