As Juan said, But easiest way to access that is by going to the files tab in the channel, then clicking "Open in SharePoint" link on the toolbar. Then on this page, you can select the files you want to share and click share. If you want to share the whole folder, you can back out a level by using breadcrumbs at the top, then select the folder, and select Share.
This functionality will be coming directly to the Teams File tab one of these days, when they release the SharePoint UI for files tab.