Hello Ping Wu,
I was reviewing the configuration files and there is a separate MACHINE for each of the two silicon versions supported:
imx8qxpmek for the B0 silicon
imx8qxpc0mek for the C0 silicon
So please bake the recipes you need accordingly. I would recommend having a separate build directory for each instead of using the same one and changing the local.conf file, as to avoid issues when baking.
I hope this information helps!
Regard!