Section 6(1)(b) in The Companies (Mediation and Conciliation) Rules, 2016
(b)Where, there are two or more sets of parties and are unable to agree on a sole mediator or conciliator, the Central Government or the Tribunal or the Appellate Tribunal may ask each party to nominate the mediator or conciliator or the Central Government or the Tribunal or the Appellate Tribunal may appoint the mediator or conciliator, as may be deemed necessary for mediation or conciliation between the parties.