I want to specify exit node to a specific country. which file is needed to be edited to make it?
You can edit your torrc.
sudo nano /usr/local/etc/torrc.d/50_user.conf
Then add the exit node(s) you wan to use. As per: Tor Project: manual
A list of identity fingerprints, country codes, and address patterns of nodes to use as exit node---that is, a node that delivers traffic for you outside the Tor network. See the ExcludeNodes option for more information on how to specify nodes.
Keep in mind this will degrade anonymity. You should not use a static exit node for any length of time. By default Tor changes exit nodes every 10 minutes or so.