Hello,
Thank you for contacting us and sorry for any inconvenience that might have been caused due to that.
Please try to follow the steps from this URL and see if that works for you: https://rankmath.com/kb/edit-htaccess/#htaccess-not-found
However, if your site is using the Nginx server, you can ignore that message in the Edit .htaccess option from Rank Math. Because Nginx servers don’t use .htaccess file. The server rules are managed in the server configuration file.
Hope that helps and please don’t hesitate to let us know if you have any other questions.
Thank you.