FYI - I just did this ...it took over a week to get an email for using the credit.

TWO BIG CATCHES - 1- It must be redeemed via Phone (no online or ticket counter) and thus there is a $10 fee...2- It can only be used to a NEW ticket, its not applicable for changes/exchanges/add-collects.

Here are the terms from the email:

Your above ticket has been reissued to the new lower fare. This credit
is valid one year from the date of issue. Credit is valid on Alaska and
Horizon operated flights only, not valid on partner airlines. This credit is
not valid for change fees, internet only fares or any other services. Any
excess amount will be forfeited. Not redeemable via the internet or airport ticket
counters. A 10.00 ticketing fee applies.

Credit must be redeemed by calling Alaska Airlines at 800-426-0333 or
HorizonAir at 800-547-9308.