You can get your credit back after you have validated a campaign you have been accepted to, or if you are not selected for a campaign you have applied to.
After you have been accepted to a campaign, you can validate it by following the instructions given in the description of your campaign. You will find all this information in your "Orders" tab. Your credit will be reallocated to you right after this validation.
If you want more information on this subject I invite you to watch our YouTube video explaining how credits work.