Hello Vishakha Dakhane
You have to enable the direction control in the RS485 control register. Then configure the corresponding pin for UART direction control function and connect to the RS485 transceiver.
That's all for RS485. The rest is just normal UART operation.
Please refer to chapter 15 "LPC176x/5x UART1" of LPC176x/5x User Manual to find the register description.
https://www.nxp.com/docs/en/user-guide/UM10360.pdf
Also you can find a reference code in this community post
https://community.nxp.com/thread/455827
Let me know if this is helpful.
Best regards,
Omar