حَتَّىٰ إِذَا كُنْتُمْ فِي الْفُلْكِ وَجَرَيْنَ بِهِمْ
Until, when you are aboard ships and they sail with them.
«كُنْتُمْ» addresses the participants, while «بِهِمْ» speaks about people in the same narrated situation in the third person. The shift changes the angle from direct involvement to viewing the event as a scene.
It is a second-person → third-person example. Its relevance lies not simply in changing pronoun endings but in recasting how the event is presented to its audience.