This charge could be caused by two different reasons as Enchant tickets vary in price.
Reason 1:
If you purchased a ticket and are moving from one ticket date to a similarly priced ticket date , then the fee is the Change Ticket Fee which is charged $3 per ticket.
Reason 2:
If you purchased a ticket and are moving from one ticket date to a higher priced ticket date, then the fee is the Change Ticket Fee of $3 per ticket plus the difference in ticket prices.