Hi Lukas!
Thanks for reaching out, and thanks for using BoldGrid’s WordPress website builder.
Unfortunately our plugins and themes do not have the ability to change the items displayed in a menu when a login session is detected. However our plugins and themes operate within a WordPress environment which allows you to use a wide range of additional plugins to help create the behavior you are looking for on your website.
I located a plugin in the public WordPress repository called User Menus which looks like it will allow you to change the visibility of your menu items for your logged in users.
Hopefully that plugin helps you achieve your design goals and please let us know if there is anything else that we can do to assist you!