This tutorial uses an Allen Bradley Panelview Plus 6 as an example.
Follow the iOS VPN Setup KB article here first
1. Visit the App Store and download Mocha VNC ($10 app)
2. Open the App and select Add another Server, Press New…
Enter the following details:
IP Address: <IP address of your HMI>
VNC Password: <password set from within your HMI> (optional)
Alias Name: <Name of your plant>
32-bit color mode:OFF
3. Now press Connect
4. To exit, press up arrow then the 4 horizontal lines icon, then select Disconnect
5. Open Settings and Disconnect the VPN Session