Existing SharePoint sites can have a Team created in Microsoft Teams.
Adding Microsoft Teams Integration
Open SharePoint in your browser.
Open the homepage for your SharePoint site.
If the site is not linked to Teams, a popup will appear in the bottom left after the site finishes loading.
Click Add Microsoft Teams.
In the window that appears click Continue.
If desired, select Folders from the SharePoint site’s Documents to pin to the top of the Team for easy access.
Click Add Teams.
Open Microsoft Teams and you will a new Team created with all the members of the SharePoint site.