Tenant is set to “New Experience”, user needs classic experience, selects “Return to Classic SharePoint” does what is needed and wants to return to Modern view, but there is no switch or link to return to Modern view.
Reason for Issue
A session cookie is created to change to Classic View, and in time the cookie will expire but if needed before the expiration date, cookie’s and cache will need to be removed.
Clearing cookie to return to Modern View.
Select F12 to bring up the developer tools at the bottom of the window.
Select the 1. Network Tab >2. Clear Browser Cache > 3. Clear Cookies for Domain > 4. Clear Entries on Navigate (If not in private browsing this item will not deselect). > 5. Clear All entries.
Close the development window > Refresh the Page “F5”. This may take a few minutes, in extreme cases can take up to 5 days, once the cache and cookie’s are cleared the page layout should return to “Modern View”
Internet Explorer: https://msdn.microsoft.com/en-us/library/hh968260(v=vs.85).aspx
Microsoft Modern View and Classic View Info