Seed mp157c SOM boot_device doesn't change mmc from usb

[U-boot]
STM32MP> print boot_device
boot_device=usb
STM32MP> boot_device=mmc
STM32MP> print boot_device
boot_device=usb

I made my custom seed mp157c SOM mpu module base on Odyssey board.
but some reason the ‘boot_device=usb’ fixed.
I want to change to ‘boot_device=mmc’ .

how can I do that?

I think there would be any gpio pins have to go HIGH or LOW

at u-boot console , ‘save’ or ‘save env’ doesn’t work!
need help please