You can either mount your SD or EMMC on a computer and replace dtb.img with the correct file from the device_trees folder or use the commands below via SSH.
mount -o rw,remount /flash
cp /usr/share/bootloader/device_trees/g12b_s922x_odroid_n2.dtb /flash/dtb.img
reboot
The countdown is there to make users aware that they need to update the device tree because there is an update for it.