My left rear window does not roll down, though it does roll up.
The electric motor for the window is used to move the window up and down by a switch that can change the voltage direction to the motor. If the motor works in one but not the other direction then the switch is the most likely defective part. I would recommend having a mechanic, like the certified ones at YourMechanic, come and check it out for you to see if this is the only problem.
Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing