Knobs installed wrong

I have a Jenn-Air cooktop with double flat type shafts on the infinite controls. I have a cleaning service who removed the knobs to clean the cook top and somehow managed to put two of the knobs back on upside down… I assume they had to use quite some force…

When I attempted to remove the knobs to correct the situation I managed to snap both shafts. I ordered replacement controls and knobs and "fixed" the problem.

To avoid such a costly repair in the future… does anyone know how to remove the knobs without breaking the shafts in the future?

Thanks