Hi! Reece,
Of course open App Security > Demo user first click enable demo users Yes to access demo users and their properties.
First View you app and second Sign in it as the Administrator
Then click a user icon in the right side of the screen. The menu bar Select user will be displayed. You can log in to the module you want from here. Also you can read https://docs.mendix.com/refguide/demo-users/ ot this documentation.
Good luck with Mendix
Kind regards,
Mehmet