edit audio files

I am looking for a skilled audio editor to work on multiple voice recordings for an audio book. I have recorded them and edited them in garage band, however they failed the Amazon ACX upload due to RMS range not being in compliance. The "RMS range" must be between -23db and -18db. I need some help editing that. It needs to be uploaded into Amazon (ACX) as .mp3 format. Total record time is ~3 hours over 12 chapters and 1 preview file. If you are experienced in audio editing, I would greatly appreciate your help to make these voice recordings perfect! NOTE: This is a Christian-based marriage book, FYI. See example attached. I can of course use Dropbox (Google drive, etc.) to share either the .mp3 or Garage Band files.