Bootmagic reset: Hold down the key at (0,0) in the matrix (usually the top left key or Escape) and plug in the keyboard
Physical reset button: Briefly press the button on the back of the PCB - some may have pads you must short instead
Keycode in layout: Press the key mapped to QK_BOOT if it is available

Make example for flashing this keyboard (after setting up your build environment):

make onekeyco/dango40:default:flash

See the build environment setup and the make instructions for more information. Brand new to QMK? Start with our Complete Newbs Guide.