No Robots.txt editing box in Edit files section

Hi, I wanted to add/edit the robots.txt but I cant do it because there is no editing box for robots.txt, it only have a box for editing .htaccess file as shown in this screenshot.

Please help me how to make the robots.txt editing box avalable. Or did I just missed something? Please enlighten me regarding this.

Thank you in advance 🙂

https://wordpress.org/plugins/wordpress-seo/