Getting your tile redone is a pain in the butt if you have no idea what you are doing. First you need to find out what type of tile it even is. It could be natural stone, travertine, marble, and even granite. This is just the first challenge. There are many different steps to take to repair tile depending on what type of tile you are dealing with. A lot of amateurs will install tile the wrong way which can make your house or business place look pretty terrible. Here are a few steps to make sure that things go smoothly when repairing any type of tile.
Typically you will need the following 8 things: Old rags(you wont be able to reuse them after this), spray bottle, good supply of water, thin scrub(toothbrush will work), one large sponge, one grout float, one grout saw and last but not least, a lot of patience and precision.
Step 1: Go to the store and buy some grout(if so needed)
step 2: Remove rotting/loose/damaged grout
step 3: spray the area with spray bottle and brush down with toothbrush
step 4: mix up the grout
step 5: spread grout where you just cleaned
step 6: make tiles squeaky clean
step 7: polish all of the tiles
This is a very brief overview of how tile repair goes for MOST tiles. As I said each kind of tile is different, but this is the most basic way you that you will find. I wish you the best of luck in your tile repair endeavors!