Hi @Mohd
Have you seen this reference link?
There are two ways to enable Rs485 communication. One is from Devicetree and the other is from userspace.
In which file it is located?
Clone the Linux kernel and alter the Devicetree file arch/arm/boot/dts/vf-colibri.dtsi,build and update to existing Linux image.
For building and updating the device tree, please have a look at this article