There is no magical method to rewind time in unity. You need to do it yourself.

Little hint : every x amount of time, add the current position of each object you want to rewind in their own specific "previousPos" collection (i.e a list, or even better, a stack), then gradually move them back to their previous positions when you want to "rewind" time.  Don't make the collections infinite though, make it only store the last 20 for example.