How do you fix a Vornado speed knob?

I bought a two Vornado 783s in 2015 (just out of warranty) and they are going strong with no maintenance. However, the speed knob detached internally. The speed knob is still attached, but it now winds 360 degrees and no longer turns on the Vornado. There is no more resistance so it seems the knob is still attached but whatever it is attached to is detached from the motor or power unit inside.

How do I fix this? Do I pull hard on the speed knob so I can see what is wrong and attempt to reattach whatever has been detached inside?