In the sermon on the mount Jesus talked about resolving disputes by “taking it to the church” (literally “assembly” of believers) so there was some concept of church during his ministry. Church means “assembly” (of people) though, the greek word really bears no resemblance to the modern idea of church as a building with a carpark.

I feel that’s probably among the genuine sayings of Jesus because later editors have declined to inject verses supporting bishops and elders which was surely tempting to do.