how create EndLess game Like zombie Tsunami

I’ve created a 2D game with a list of objects with their location

When one of the objects is destroyed ( their locations are released )

So how do the object front may move up and replace the position of the object has been destroyed
Sory my English

Hi, I saw your post I’m making something like that I just want to ask how did you made the player’s movement? You know, the players behind you replay the first player movements.