To install a new knob first soak in hot water. This softens the plastic slightly and also expands the opening.
The flat end of the knob is slightly thicker on on side - that side goes away from the steering wheel, The knob is installed at the same angle as the steering wheel....the reason for the is that the shift lever can be moved with just your finger tips without taking your hand off the steering wheel (if vacuum is working OK)

I have a few new genuine new knobs in stock for $10 + shipping (in the US)