[Worked] Wan vs usb therering

I have wndr4700 I use wan and 4g usb therering for internet, sometime my wan become slow or dissconted in that case I insert 4g usb therering for fat internet.
But i have go to>Inteface>stop wan
so to work 4g usb therering
I there a methord, so that when i insert 4g usb therering then it diasble wan
when I remove 4g usb therering it shoud enable wan

in short
insert 4g ==> disable wan
remove 4g ==> enable wan

try to increase metric for wan interface, so 4g connection will be prefered if available

Use mwan3 in a "failover" configuration.

I think this will work only when my wan dead but not when my 4g is inserted

I cant find any place from where i can change metric value Interface.
I have installed mwan3

but I get in mwan3

MWAN Interface Configuration
There are currently 2 of 250 supported interfaces configured

WARNING: some interfaces have no default route in the main routing table!

WARNING: some interfaces have no metric configured in /etc/config/network!
MWAN supports up to 250 physical and/or logical interfaces
MWAN requires that all interfaces have a unique metric configured in /etc/config/network
Names must match the interface name found in /etc/config/network (see advanced tab)
Names may contain characters A-Z, a-z, 0-9, _ and no spaces
Interfaces may not share the same name as configured members, policies or rules

but I can see lots of warning and error
mwan3>troubleshooting> https://pastebin.com/ysnz8AGA

thanks both of you