After the installation of the Drupal module Redirect there is usually the tab "Fix 404 pages" under "URL Redirects". As the designation indicates this function allows you to redirect 404 pages. If this tab does not appear it usually has a very simple reason: The Drupal core module "Database Logging" is not enabled. Being able to reconnect 404 pages, the 404 pages obviously need to be recorded and that's done by the core module "Database Logging". Enable this module and the tab will appear. Please note: The 404 pages are of course only recorded from the moment this module is enabled.