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 begins setting up the board as the macropad. In Arduino IDE, the board isn't detected because of this, and the "Ports" tab is grayed out. When doing a double reset, I'm able to see the board at COM3 for a very brief moment, but even after quickly hitting "burn bootloader", the PC begins setting up the macropad and Arduino IDE fails to upload anything.

Any advice?

What is macropad? Where did you get the hex file from? What is QMK? Provide links to the stuff that you have used.

How did you flash the hex file? Via USB or via ICSP?

If the latter, you will probably need to burn the original boot loader.

What happens in Windows device manager when you reset the connected board? Does it show a port with "boot loader" in the title?

What you can try
Select the com port in the IDE while you can; it does not matter which port you select. If you have another Arduino or so, connect it and use that port.
In file -> preferences in the IDE, enable verbose output during upload.
Connect the ProMicro while keeping it in reset.
With ProMicro still in reset, compile and upload.
When the IDE reports the memory usage and starts spitting out line like {COM x, COM y} => {}, release the reset button.

Sorry for leaving out key details -- but your solution worked perfectly!! Thank you so much!