how do I add a favicon to RSS feed in Bitnami Drupal?
You can try to modify the line 1611 of the file installdir/apps/drupal/htdocs/includes/theme.inc. Change feed.png for the name of your image previously placed in the folder installdir/apps/drupal/htdocs/misc/

The original line is:

  if ($image = theme('image', 'misc/feed.png', t('Syndicate content'), $title)) {