Mediation is a process for resolving conflicts among several entities. In argumentation debates, conflicting agents that may be organized as teams exchange arguments to persuade each other. In this paper, we consider an automated mediator , which assigns the speaking slots to agents so as to optimize some objectives and ensure the fairness of the debate. We propose a general setting where the argu-mentation strategies of the agents are probabilistically known and may evolve over time. We show that the problem can be solved as a semi-Markov decision problem with hidden modes.