If you can drop files in to this version of Cubase then export your 4 tracks from the OP-1 (maybe on to a computer first) then drop them in
I don’t know how the iOS Cubase is, but you could also record each in the same way as any external audio with an audio line in from OP-1’s output. You’ll need to manually line up the tracks. You could do this by recording a short sharp sound on all four tracks in the same place on the OP-1 as a reference to line the tracks up, just like a clapperboard is a reference for lining up audio and visual recordings for film.