where is my robots.txt? how can I edit it?

Google webmaster tools shows that “Text of https://www.mydomain.com/robots.txt” says “User-agent* Disallow:” I need to change this but I don’t see robots.txt on my root directory. My hosting support says “The URL is generated using the rewrite function of your WordPress.” Where is my robots.txt? or how can I edit it?

I am not sure if this is relevant, but my WP files are at https://www.mydomain.com/site” and I don’t see robots.txt there either.

Any help is much appreciated!