This credit scene would take place after the Justice League defeats Brainiac in the first JL movie.
After their tough battle with Brainiac, a wormhole opens up on the outskirts of Metropolis. 7 bodies appear after the wormhole vanishes. We see the backs of these 7 mysterious bodies. The one in the middle steps foward and speaks.
"We made it, we have finally made it. After years of searching the infinite universes, we have found Earth-Prime."
He turns, (we see a owl type suit) and says,
"Ultraman, what is next?"
We now see a close up of Ultraman. He stands there and says in a menacing voice,