Adding OpenWrt support for Xiaomi AX3600 (Part 1)

In the current state, safe is not. But I have been looking for information and several boards have double uboot, such as

This model has everything in duplicate. What I don't know is how to choose the second uboot. If we knew how to force the second uboot to load, we could keep the original uboot and test the secondary one, without the need for Jtag. Looking for other bootlogs on the internet, there are other models with only two uboot, and the rest of the partitions like ours, others with two uboot and two uboot_env, etc... I think the double uboot mechanism exists, if we find out how it works, it will could try.
uboot is referenced like appsbl and the second uboot is appsbl_1
Do you think this information is correct?