@TONG, JASPER That appears to be the name of the subscription that the training author has for their specific Azure subscription. Just like how you named your subscriptions as shown in your screenshot, the author of the training you are following called his Azure subscription Concierge subscription.
I would select a subscription that you are comfortable with having these training resources created in. If your three subscriptions that it appears you currently own are not ideal to have training resources located in them, you can always create a new subscription for your training.
Here is a link on how to change your subscription name if you prefer to have the subscription you select match the name provided in your training doc.
Please let us know if you have any further questions or concerns. Best of luck on AZ-900.