Per https://help.prusa3d.com/article/xbuddy-and-loveboard-electronics-wiring-mk4_413095 it looks like you dont have any fan headers, you might be able to repurpose the unused ambient sensor header but no clue sorry. You might try splicing off the part or hotend fan? If you really wanted to use the dc input you might need a voltage step down buck converter or something depending on what your PSU is putting out