Erease code from Arduino

[alto777]

If you've made it into a USB device, you may have to go a bit out of your way to reprogram it.

I googled

 can't reprogram usb pro micro

and found

SOLVED: Completely resetting Arduino Pro Micro

First post here, I have a SparkFun Arduino Pro Micro soldered to a 4x4 macropad. I previously flashed the Arduino with a .hex file (compiled through QMK) for the macropad, and it works great. The only problem is that I have connected other SparkFun devices to the Arduino now, and I want to reprogram it to handle more than just keypresses. I've tried pretty much everything to reset the board (uninstalling drivers, "double" resetting, etc.), yet everytime I plug it into my PC, my PC immediately …

which may be your issue.

If it's not a help, google along the same lines, I just post the first one that looked plausible.

a7