Recommend you check out the appropriate Mac or Windows "MX920 Series User Manual" found at the Support Page. The files there are unfortunately not PDF (you'd need to run either the downloaded Mac or Windows installer). Thus I don't have any specifics. However, try searching the manual for reset which should hopefully outline what you can do to perform a factory reset.
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Ricky
Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers
