Okay so in their story Oz shows up during what I call Lisse’s Second arc. It takes place a few months after her coronation too become the Queen of Hearts, while she’s struggling too adjust too her new role plus the trauma of the tournament.
She wanders too the altar she had initially woken up on in the rose garden where she finds a man looking around. It was Oz! By chance he returned too the world of Wonderland, curious too see how things worked out since his past intervention (though Lisse doesn’t learn his role in everything for a while)