Switching Wireless Networks in Lockdown Mode
Unfortunately, I have no Zebra TC57 device on hand to perform any test. If the list of Wifi networks does not go away to the left when you do not have kiosk mode enabled, then maybe you should try to find out the app bundle-ID/activity name that is responsible for showing the list without the kiosk mode. If found, try to add it to the kiosk/kiosk-whitelist.
You could add settings manager to your lockdown and enable access to Wi-Fi.