See [build environment setup](https://docs.qmk.fm/build_environment_setup.html) then the [make instructions](https://docs.qmk.fm/make_instructions.html) for more information.
STM32F042xx chips does not allow jumping to bootloader without BOOT0 being set to high, therefore it is impossible to enter the bootloader from sending a `QK_BOOT` keycode nor using bootmagic or bootmagic lite.
The only way to enter bootloader is to hold the BOOT0 button while the keyboard is powering up or after a power reset (done by pressing the reset switch or sending a `QK_BOOT` keycode).
