I lent my, and yes last time it will happen EVER, Prius to my brother for a week and when it came back he pointed to the radio and said "the tuner knob won't turn anymore". Well, not only that, but he pushed it in, so I can't even get it out to turn it.
Trying to remember back to my 2008. Seems as though there should be a slight indent when you press the button in, and it should release some more button travel outward so you can turn the knob. I never removed these knobs in my car, you know, to remove dust and other foreign material. So I don't know if any amount of careful prying might return it to service. Can you turn the knob in its present location?