Good Morning Khalid,
I’m glad you’ve enjoyed working with the theme. It is possible to remove the WordPress editor that’s in the appearance section. Some web hosts do that automatically as a security measure and also to keep users from accidentally locking themselves out of their websites.
In the root folder of your WordPress site there is a file called wp-config.php. Most likely there is a line in it like this:
define( 'DISALLOW_FILE_EDIT', true );
If you find it there you can change the true to false and save your changes. That should bring back up the editor for you.
That said, with editing theme files it’s best to edit them locally on your computer and upload the changes via FTP. You can create/find a FTP account in your web host’s control panel. Once you have those credentials you can use a FTP program to to upload changes you make. That’s usually the best way to go about making edits.
Let me know if I can help,
Bill