Once you connect to the IoT Box with the Odoo instance, you cannot use that IoT Box with other Odoo instances. If you try to scan for the IoT Box and it is already configured, a warning icon will be displayed:

If you want to connect an existing IoT Box with any other Odoo instance, you will need to clear the configuration. You can clear the IoT Box configuration with the Clear button in the Odoo server configuration page of the IoT Box: