When a rocket is in space and needs to return to Earth, it has to push off something. But there is no air in space for the rocket to push off of. How will it return?

It uses the rocket propulsion method to get the required thrust to reach Earth's gravitational field.

Explanation:

The rockets that reach the zero gravity line has nothing to push off to get thrust. So it seems that it is violating the Newton's 3rd law of physics i. e each and every action has its opposite and equal reaction. But its not the case.

The rocket has fuel in it. It burns the fuel inside it. Thus the mass of the fuel is burnt inside the rocket which propulses the fire through the nozzle in a particular direction. Thus the mass of the fuel lost is forced in a particular direction which gives the thrust opposite to that of the nozzle direction. And in space, there's no friction. So no force is lost to overcome it. Thus, the rocket gets enough force or thrust to return into Earth's gravitational field from where the gravity takes up the upper hand to pull the rocket itself.