Fan will not oscillate
I agree with Ed Beal, if the plastic gears are stripped, there is no practical way to replace them. But did you check to see if there is a plunger that is INTENDED to engage / disengage the oscillation? Some designs have that, some don't. On those that do, it's usually set up that you pull UP to engage the oscillation, push DOWN to disengage it. So when moving the fan, if you accidentally pushed the plunger down, you inadvertently turned off the oscillation. In the image below, the oscilation plunger is the device on the left.