you mean the source file is
bootloader/t186ref/BCT/tegra234-mb1-bct-pinmux-p3701-0000.dtsi
can be copied to
bootloader/tegra234-mb1-bct-pinmux-p3701-0000.dtsi
so i should modify the file
bootloader/t186ref/BCT/tegra234-mb1-bct-pinmux-p3701-0000.dtsi
OK, thanks, i will try