Geometry modification
 

I am new to CFX. I've a geometry that was given to run simulation but I'll like to make some modifications to the inlet which is just adding like face or wall to it to reduce the inlet.

How can I access the geometry with already mesh in place?

You will need to load it into a mesh editor such as ICEM. In general this is a bad idea and you will want to remodel the geometry and remesh.