Not clear if this is a targeted offer to selected Concierge members but seems like its in addition to the yearly 3 X $20 credits
To claim your $20 store credit in store or online use the code provided in your SMS during the promotional period.
Or
To exchange your $20 store credit for $60 store credit, all you need to do is spend $300 or more in store or online during the promotional period and not use your $20 store credit. We will do the rest. We know you are a Concierge customer and when you spend $300 or more we will automatically send you your $60 store credit on 10 August 2017 via SMS.
Did you receive the SMS with the code? If so, does it look generic? ;)