Connect the specified site collection to the specified hub site

• command: spo hubsite connect -h|--hubSiteId <id> -s|--siteUrl <siteUrl>
• id: hub site ID
• siteUrl: absolute URL of the site collection to connect to the hub site
• requires connection to the SharePoint tenant admin site

For more information see the Connect-SPOHubSite cmdlet in the November release of the SPO PowerShell.