How can i attach the XREF file?
Go to toolbar menus click on insert then on the 11 item from the top to the bottom you can find a command "Xref Manager" then click on it and you can find a chart there and on right side of the chart you can see a button says "Attach" then you can proceed to do attach the Xref drawing to the you you are working on.
Hopefully this instructions will help you a bit.