Very difficult trial and error. One motor at a time. Mark one side of the prop with a marker. Plastic electrical tape on one side or the other. Use accel and gyro scopes to help see if it is better or not.
Or find a straight, smooth metal shaft the right diameter to at least get it close.
When vibration causes stabilization problems, it usually causes tilt, but not oscillation.
Or find a friend that has one. Get one ordered today so it gets here quickly or buy one from a model store.