Microsoft Teams sites are created using SharePoint Pages, and SharePoint Pages provide the ability to embed content from other sites (like LibraryH3lp) using "Embed Web Parts." The only issue is that Embed Web Parts cannot include JavaScript, which means that you can't use the embed code for a LibraryH3lp chat snippet. BUT you can embed iframes as Embed Web Parts, and the LibraryH3lp chat box works great as a simple iframe. Here is a how-to help doc that Microsoft provides to walk you through adding iframes as an embedded web part.