Start with a pep talk through the order of patterns:
Announce when the treble is leading to begin with (might have to even if the learner is ringing the trebles).
Start with one lead at a time. If it fires out, start at the previous lead end.
Don’t always start at rounds, practise the tricky bits by starting at the middle lead ends or at a roll-up or at back-rounds.
If you get really stuck, watch the videos.