By default GPIO 50 and 51 are routed to the RX and TX pins respectively. You will need to set GPIO 40 and 41 low to route UART to the RX and TX pins. Also there is a level shifter controlled by GPIO 4, this needs to be pulled high.
Thanks for replying.
what should i do to set gpio40, 41 and gpio4 to low? by hardware jumper or need to write software to set it?
No need. thanks your kindness.