To change the port to the BT UART (higher RS232 connector on the evaluation board) type in the bootloader menu:
x set set ser.port = 0x40200000 save ser
Select one of the ports by assigning 1, 2 or 3 to ser.port . 1=UART A 2=UART B 3=UART C as defined in the SO-DIMM/MXM3 pinout.
x set set ser.port = 2 save ser
It is not possible to use an other pin mux setting than the default one in the bootloader.