There are specific rules for which division may hear particular types of action. The UPC jurisdictional rules reserve some actions for the central division and others for the local/regional divisions, and are quite complex.
However, broadly speaking (and there are exceptions) stand-alone revocation actions and actions for declarations of non-infringement, both without any counterclaim, would normally be heard in the central division in Paris, London or Munich, depending on the technology of the patent in suit.
Infringement actions are generally (again subject to exceptions) to be heard in the local/regional division in the state where the alleged infringement occurred or in the state of the defendant.
In cases where there are linked claims of infringement and revocation/non-infringement the relevant judges must decide whether to hear all the complaints together in one division or to hear the different complaints in different divisions.
Within the rules there may be some limited possibility for the party bringing the action to choose the division, e.g. where infringement occurs in several states. The defendant may argue that the action was brought in the wrong division.