@kyson-lok

config forwarding
	option dest 'ovpn'
	option src 'guestzone'

YES!!! WORKING!!! THANK YOU!!!

I have working now but you must know GL UI continue have many troubles. I do reset the router to factory settings but every problems is same. If I make WiFi client to connecting modem I will not see no options for WIRELESS, nothings completely only white page does not say nothings.

After I do this to /etc/config/firewall like you are saying and now I am see 2.4G WiFi where I click WIRELESS so I think maybe you have problems in GL UI because it not support WISP configurations if using OpenVPN.