If you are already using SharePoint Online Communication sites, would have noticed that its not showing up in the SharePoint admin center to manage or its not listed in Office 365 admin center. So there is no option as of now to manage these sites through UI, until the most awaited new SharePoint admin center is rolled out.
The below script will help you to add yourself as a site collection admin to all the communication sites in the tenant and avoid the annoying access denied error for SharePoint admin/Global admin. PowerShell script uses SharePoint online management shell, so make sure to install it before you use the script.
Use the below script
# Update the tenant url
PS C:\> .\Add-CommSitesSCA.ps1 -Url https://<tenant>-admin.sharepoint.com
## Or Provide optional credentials
PS C:\> $creds = Get-Credential
PS C:\> .\Add-CommSitesSCA.ps1-Url https://<tenant>-admin.sharepoint.com -Credentials $creds
Download the complete script from here
Peace!