The option for table assignments can be enabled in the event settings page. You can access this page during the event setup, or by editing an already existing event. While editing or creating a new event page, the slider can be set to enable table assignments for that particular event. Additionally, if "use seating chart" is set to 'yes', the option to enable table assignments will not appear. Thus, to simply find the option to enable table assignments, change "use seating chart" to 'no', and the option for table assignments will appear.