I would have a look at this tutorial for steps on how to open and perform an atmospheric correction with FLAASH in ENVI:
http://www.harrisgeospatial.com/docs/...
After atmospheric correction, you can georeference the data using the geometry bands that typically come with AVIRIS data (called IGM or GLT bands). You can use the Georeference from IGM or Georeference from GLT options in ENVI.
https://www.harrisgeospatial.com/docs...