When using a microcontroller like the Pro Micro or the Elite C, it's always helpful to test it before you solder it to your keyboard. This way, if it doesn't work, you won't have to go through the effort of desoldering it, and can return it within the warranty.
So, how do you know your microcontroller works?
Connect the Microcontroller to Your Computer
Plug in the microcontroller to your computer. For the Pro Micro, use a Micro USB to USB A cable. For the Elite C, use a USB C to USB A cable.
If your computer supports USB C, it is of course fine to use a USB C cable as well, as long as it supports data transfer as well as power.
If the power LED lights up, then that's a good sign already!
Flash the Microcontroller With Your Keyboards' Firmware
While the power LED is a good indication that it works already, it doesn't mean everything. If you're able to flash firmware to your microcontroller, that's a more sure way to verify that it'll work in your build.
To flash your microcontroller, I recommend following QMK's Complete Newbs Guide to flash it with your keyboards firmware. In case of the Kyria, you can follow the following article: Kyria Build Guide: Kyria Firmware.
To reset a microcontroller while flashing, short the RST pin with the GND pin. You can use a pair of metal tweezers with one leg on the RST pin and the other on one of the GND pins to short them together. This has the same effect as pressing the reset button.