You need to put the search, release and transfer steps into the Add-on Process Triggers "Parent Entered" of the Combiners.
For example, for the "Juntar_secos" combiner, at the "Parent Entered" Addon process, you would search for Slots.Processing.Contents, matching "Candidate.ModelEntity.Id_Del_Pedido == ModelEntity.Id_del_pedido". After that you should use a release step, to release Server "Slots", and a transfer step to transfer what have been found to Output@Slots.