You literally uploaded this video RIGHT AS I GAVE UP ON LOOKING FOR ONE. I just got done asking someone in-game to teach me. Still liking the video though, because more people need to see this
In this situation you need to turn on emergency diesel generators (which takes a while) and then redirect power from power grid to generators. That way you can use LPCI when RCIC has filled Reactor to a specific level and when pressure inside reactor is low enough for LPCI to operate. Also, activate offline cooling immediately after getting power from gens.