러 들어오다

come in to do something

"-(으)러" marks the purpose of a movement and 들어오다 is "come in", so the whole thing is "came in to do X". Both scales of coming in are here: entering a room or a livestream — came in just to see your face, came in to do the challenge, Trump coming in to give a speech — and entering a country or a job: coming in to attack, Japan coming in to occupy, coming in to work, coming in to serve someone. Compare 러 가다, the same purpose ending with "go" instead of "come".