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Hi Nageswara,

>>>>>While using it I did not find EXPRESSTOOLS in ribbon.

>>>>>Wondering can I install/activate this particular menu item.  

There is no Ribbon in AutoCAD for Mac.

You can find all Express Tools available in AutoCAD for Mac in menu Tools->Express Tools:

They are ready for use without additional installation options.

Note, that not all Express tools from PC version of AutoCAD  available on Mac.