Xplane 12 Unable to connect GTNXi 750 in standard C172

[Flying Squirrel]

I know this is a simple fix.  I just can't figure it out.  Purchased the GTNXi for Xplane 12 today.  Download went fine.  Able to properly install in my Viper Jet.  Not able to get the 750 to show on the Xplane 12 standard C172.  I get the pop out via the plugin page, but I can't figure out how to get the unit to replace the existing avionics in the aircraft.  What am I doing wrong??