To enter the bootloader, short the rst and gnd pins with a conductive material such as a tweezer or a wire. Uni v2 will have reset pads next to the pro micro so you can short these pads to reset the pro micro.
See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).