After update OpenWRT, no boot from nand possible

After updating the Banana Pi R3mini on eMMC as decribed in OpenWrt-Wiki, the device does not longer boot from NAND.

Now i booted from UART while switch is set to eMMC.  I tried:
mtd write /mnt/usb/openwrt-24.10.3-mediatek-filogic-bananapi_bpi-r3-mini-snand-preloader.bin /dev/mtd0
Could not open mtd device: /dev/mtd0
Can't open device for writing!

What is to do, that the device can boot from nand again?