To modify/add directives to the .htaccess file in your public_html directory using "File Manager", follow these steps:
1. Log into your cPanel account.
2. Click on the "File Manager" icon.
3. Click on the folder icon next to "public_html".
4. Click on the file named ".htaccess".
5. In the left hand window click the "Edit File" link.
6. A second window should appear. Type or paste the code you wish to add into this second window.
7. Click the "Save" button.