Go to DHCP Table under Diagnostics and copy the IP ADDRESS
Go to NAT > Port Redirection > Choose a Port
Settings
Mode: Single
Service Name: Kiosk
Protocol: TCP
WAN Interface: ALL
Public Port: 5995
Private IP: Paste the IP ADDRESS from DHCP Table
Private Port: 5900
Open VNC and enter public IP address with 5995. i.e. x.x.x.x:5995
Password: secret