I'm sorry man. I have this xiaomi router with openwrt installed but I'm not using it as many things just don't work. It was my beginnings with OpenWrt.
Usually routers have 2 partitions. When you install openwrt on one, second have original firmware installed. To boot from second one you have to reset router. From router to router this my be different, but try to unplug router, hold or use pin to reset router for 10-15 seconds and plug router in. Sometimes you have to hold a reset button when you plug router for 3-5 seconds to force it to boot from another partition.
Again, I'm sorry.