In db https is used for home, but in backend http is used and cannot be edited

It is possible to hardcode the value of the “WordPress Address (URL)” and “Site Address(URL)” options within your wp-config.php file. When the value of either field is hardcoded this way, it takes precedence over the respective value set in the database. This is why you cannot edit the field via the WordPress Admin Page ( the value is hardcoded ).

My suggestion to resolving your issue is this:

1) Open your wp-config.php file
2) Look for a line of code similar to the one below

define('WP_SITEURL','http://www.example.com');

3) delete it

That’s it! You should now be able to edit the “WordPress Address (URL)” from the admin page.

Reference: https://codex.wordpress.org/Changing_The_Site_URL#Edit_wp-config.php