How do i fix cracked grout around floor tile?

Mix up the needed amount of grout and apply to the cracks with a spoon. Keep the solution a little thin (watery) so you can spread it easily into the cracks.

The best thing to do in your case is to remove all of the grout, and regrout the entire floor. There are different ways of doing this such as a butter knife, broken hacksaw blade, and there are also tools that are made for this specific purpose. Putting the new grout down is not complicated either. Get some grout (I prefer the kind that is premixed), and apply it with a ‘grout float’. This is just a stiff rubber pad backed by metal, and it has a handle. These are readily available and are very cheap. You get some grout on the float and sweep it at an angle across the grout lines. Make sure to hold the float at approximately a 45 degree angle in relation to the floor. As you sweep the grout float make sure you fill all of the grout lines in. You’ll also want to make sure to leave as little excess grout as possible on the tiles (this will make the cleanup easier). Once the grout is completely dry put some warm water in a bucket, and a sponge (not Spongebob) and wipe the excess grout from the tiles. Again, wipe at an angle to the grout lines. Last step...get a nice glass of lemonade and sit back and enjoy your work.

Try to clean out as much of the cracked grout you can with a knife or something thin being careful not to crack tile then purchase grout eather already made or powder and apply with a sponge and squeeze in cracks very well over fill letdry for a 24 hours wipe surface away