I installed this app for online appointments

https://apps.odoo.com/apps/modules/14.0/s2u_online_appointment/

and I need unregistered users to be able to schedule with it. The docs just say "If you also want public users to schedule appointments, create the parameter 's2u_online_appointment' with value 'public' in your 'ir.config_parameter'" which is not very helpful. I get that ir.config_parameter is a model, but I have no idea how to go about creating this value. Any help, please? Is it under access rights? Fields? I'm lost here.