how to repair the floor ?

You have to purchase the floor repair kit from the varied items in the store. You'll need a minimum of 3 kits to finish the floor. I say minimum because there is a possibility of an event in which the floors become damaged again.
Place the floor repair kit over one of the cracks on the floor. Then repeatedly place one of your little people over the crack and they will slowly repair the floor. The floor repair kit and the crack will disappear when the crack is repaired