Each private channel has its own SharePoint site. The separate site is to ensure access to private channel files restricted to only private channel members. 

A private channel site syncs data classification and inherits guest access permissions from the site of the parent team. Membership to the site owner and member groups are kept in sync with the membership of the private channel within Teams.

To reach the site settings page in SharePoint 

1. On the top right of your Sharepoint Site, click the Settings icon. 
   
   
2. Click Site Information.
   
3. At the bottom of the Site Information window, click View all site settings. 
   
   
4. You will now find the Site Settings page, with customization options including: Look and Feel, Site Actions, Site Collection Administration, Microsoft Search, Web Designer Galleries, Site Administration, and Search.