B1300 Questions!

I would like to ask something about Mesh router GL-B1300 / Convexa-B. As I’m new with this device.
I have done configure this device but I can’t change or set static DNS on the router.
It always takes default gateway as DNS.

One more thing, when I tried to add mesh extender via application Minim, it always disconnected the internet connection and without restarted the WAN interface, all of my devices can’t access the internet even I have received WAN IP from ISP. Sometimes it reverts back to DHCP option by itself.

The firmware that I got is Firmware Version:
As I have searching everyone got default IP: but I got

Did you use minim firmware on both routers?

Yes I have you minim firmware on both of the router.