You can join a Site by selecting the "JOIN" button on the Projects screen.

You will then have a text field in which you can enter a commissioning code.

Commissioning codes are codes generated from WiZ Pro Dashboard that allow to grant access to an existing site to the WiZ Pro Setup app. Each commissioning code is unique and some may contain additional information such as the Wi-Fi credentials for this installation. In that case the Wi-Fi credentials will be pre-filled in the Connectivity step of the Site project.