Open the link http://aka.ms/joinadminpreview to submit an opt-in request to Microsoft with Tenant URL and Contact email.
Learn more about the NEW SharePoint Admin Center at Introducing the new SharePoint Admin Center
Thank you to @wonderlaura for Power Hour which included this URL in audio. https://www.youtube.com/watch?v=UQBGaW-101A


Application for the SharePoint Admin Center early preview program
Important (10/18/2017): The current early preview program for the new SharePoint Admin Center that was presented at Ignite 2017 is now closed. You can still use this form to apply for future early preview opportunities. We will contact you via email and invite you to our private Yammer group when we start enrolling people again in the future.
Required
1. Tenant URL (Example: contoso.sharepoint.com)
This is the tenant you will want to receive the early SharePoint Admin Center preview on. Please provide one form entry per tenant.
Enter your answer
2. Contact email (Example: Bob.Smith@contoso.com)
This contact email will be invited to our private Yammer group once you’ve been accepted in the program. For multiple emails, please separate with “;”