hello momo_chen,
actually, it is not suggest to change UART2 (i.e. Debug UART) to general UART, because it’s reserve for kernel debug purpose.
you may refer to MB1-BCT configuration file,
please also check this Jetson/AGX Xavier Tegra Combined UART - eLinux.org for more details,
for exmaple,
$Linux_for_Tegra/bootloader/t186ref/BCT/tegra194-mb1-bct-misc-l4t.cfg
enable_combined_uart = 1;
spe_uart_instance = 0x2;