Xiaomi Mi 3G: Could not open mtd device: OS1

Hello I tried to install open WRT according to this video:

I get:

Could not open mtd device: OS1
Can't open device for writing!

In the documentation it says: n this case, your router is having a different flash layout and you should not proceed with the installation using mtd.

How can I proceed?

You need to find out which exact model is your router. There is 4A and R4A.
https://openwrt.org/toh/xiaomi/mir3g
https://openwrt.org/inbox/toh/xiaomi/xiaomi_mi_router_4a_gigabit_edition
Better follow the instructions in thw wiki page .
Regards