If you mean you can’t see the Custom Fields area in the menu, I would look in your theme’s functions.php file or search your theme code to see if you see a line that looks like this:
add_filter('acf/settings/show_admin', '__return_false');
This removes Custom Fields from the nav. But it shouldn’t block you from updating content or anything. All the custom fields menu item does is hide the admin area to modify field groups and fields within them. Not sure if that’s the issue.
