I have become a fan of Microsoft Teams but I have an existing SharePoint Online site called "Site" with a document library URL of https://xxxx.sharepoint.com/sites/Site/Shared%20Documents/Forms/AllItems.aspx. Other folks in the organization are already using that Site. I'd like to layer a new Microsoft Teams site on top of this existing SharePoint structure so that the new Teams Files tab that gets generated will lead to that old Site's existing document library. However, when I create a Teams site with my Site name, the Files tab leads to a new SharePoint Site47 URL (note the new numerical suffix), i.e., https://xxxx.sharepoint.com/sites/Site47/Shared%20Documents/Forms/AllItems.aspx. The SharePoint back end is therefore separate and distinct from my existing one. Any way to converge my new Teams Site without having to delete my existing SharePoint "Site" and start over? I understand that had I started the site in Teams instead, I wouldn't have this problem but I'd rather not have to start everything from scratch if possible.
Does the site already have a Group? If not, do that first. To do this step, there should be a link on the settings menu with the text "connect to new office 365 group. Full instructions are here.
If the Site is already connected to a Group, then when you create the Team, on the screen where it asks for a Team name, leave that blank and instead click the link at the bottom that says "create a team from an existing Office 365 group".