to know about the Allegiant change fees you have first to visit the official website https://www.allegiantair.com/ and get the more information about the change fees is given there but for knowledge let me tell you can change your ticket without payment before the 24 hours of the departure if you change your passport after the 24 hours you have to pay the change fees for more information you can call the allegiant air customer service number 866) 719-3910 or dial +1 801 630 8358.