By default the visitor start at the passervr.com/sites/start site, but you can change this.
In the PC builds (VR or Desktop) you will find a startup.json in the *_Data/StreamingAssets folder of the build. The * part of the names can be different between builds. You can edit this file with a standard text editor.
For the Android builds, you will find this file in the persistentData path. For the default Humanoid Visitor this will be something like …’/Android/data/com.passervr.humaonidvisitor/files’. For accessing this file on an Oculus Quest you may want to use SideQuest.
This JSON file has a field called startSite which points to the URL of the site which will be visited at the start of the Visitor application.
You can change this to have it point to another site. This should be the name without any extentions like .android.site or .windows.site.
For example "passervr.com/sites/grocerystore" or "passervr.com/sites/hummelo" will take you to some testing sites which cannot be accessed from the default start page.
Note also that when you visit these sites, you can add them to your Visitors favourite site list by opening the menu (left option button or Escape key) and selecting Site->Add this site. After this, you can restore the default start page for your visitor and still visit your custom Site using the favourite site list of your Visitor.