How to use credit?

[GreeK]

Hello friends, I ran a $150 YouTube ad from my AdWords account. By spending $150, I earned a $150 credit. After a 30-day waiting period, the $150 credit was deposited into my account. I even received a notification saying "You have earned a $150 credit." The crucial point is how I can activate this earned credit? I need information on how to spend it. I would be very happy if you could help.