How do I fix the window that will not roll down?

First you have to have a clue as to what's wrong. Does the motor make any noise? If so, there could be a broken cable or pulley. That requires a new regulator assembly and a good hour or two to replace it. If there's no sound from the motor, the switch could have a bad contact or the motor could be defective. Many motors have a thermal cutout built in for a safety feature. They cause more trouble than they prevent.

If the switches are in the center console, there could be broken wires between the driver's door hinges. That involves anywhere from a few minutes to patch one wire to a few hours to repair all of the wires to prevent future problems. Sometimes you can get a clue if the window works when you open the door to various positions.