When a molecular structure contains multiple models (e.g. NMR ensembles of models), the Models item appears in the 3D Structure Viewer context menu and in the Display menu on the toolbar.
To show all the models check the Select All item. To show only one model check the Exclusive item and then check the model you want to display. To show several models uncheck both the Select All and the Exclusive items and check the models you would like to display.