19.07.3 Mi Router 3

Hello. Is it possible to build firmware for Xiaomi MI Router 3 (19.07.3) with NAND. Now I'm use 18.06.4 and than installed with two files (kernel and rootfs).
https://github.com/openwrt/openwrt/pull/597 - Here I see support for Xiaomi Mi Router R3 but how I can obtain firmware? Thanks.