If you are not able to see “Editor” within “Appearance” tab, you must had installed any security plugin. I faced the same issue after installing a plugin named “iThemes Security” which “Protect your WordPress site by hiding vital areas of your site, protecting access to important files, preventing brute-force login attempts, detecting attack attempts and more.”
You should deactivate any such plugin to see the “Editor” back in “Appearance” tab. Hope this helps.
