Domixo what kind of hosting do you have ?
On shared hosting, you sometimes have a field where you can type the path to your website.
On a VPS, you can customize the Apache or Nginx config. In Apache the key is called DocumentRoot. On Nginx it's root. You usually already have one defined, you just need to add /public at the end.
If you can't do that, here are the instructions to move the files out of the public folder so that they use a more "conventional" installation method that doesn't require changing the web root https://flarum.org/docs/install.html#customizing-paths
