Check the power, port, and cable connections: Make sure the USB device is turned on and its cables are properly connected. If your computer has more than one USB port , switch the device's cable to another port. If you still can't use the device, contact the manufacturer for more information.
How do you reset your USB ports on a Mac?
Shut down the Mac and connect the power cable. Hold down Shift+Control+Option+Power concurrently for a few seconds, when the light on the power adapter blinks or changes colors you'll know SMC reset is complete. Release all keys at the same time.
How do I get my Mac to recognize my USB?
If your flash drive or external hard drive is not showing up there, go to Finder > Preferences > Sidebar, and under Locations, you need to tick the option "External disks". By selecting this option, we can make sure that the connected external USB hard drive or flash drive will normally show up in the Finder.