Assuming we are still dealing with your HP Pavilion 20-b010 All-in-One Desktop Computer, please see HP PCs - About UEFI and the Startup Menu and BIOS Settings for the Azara and Azara2 Motherboards. At power-on. tapping the "F9" key or the "ESC" key then "F9" when prompted should get you the Boot Menu. You may also have to ENABLE the "USB ports" and you may have to DISABLE "Fast Boot".
If you have any further questions, please don't hesitate to ask.
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