Think about it one step at a time. Observe everything that's happening. Try to answer these questions to locate the problem.
When you push the button, do you hear any sounds from near the door? If you pull the door open a bit when you push the button, does it go up? If you open the door fully, and push the button to close it, does it close? Inside one of the door frames there is a motor and an actuator of some kind. Does the door stay open if you open it? If you don't hear any noise when the button is pressed, perhaps the motor isn't getting power. Check your fuses. If you hear noise, but the door doesn't move, perhaps the actuator is broken. If the door opens when you pull it up a bit, perhaps there's a gear in there that is missing some teeth.
Trying these things will help diagnose the problem as a technician would at the repair shop. Once you have an idea of the problem, you can proceed to take apart the vehicle to confirm your idea. Then you can fix the problem.