@Vishal-Grover if you're just using EC2, you can use the Ubuntu guide as it's the same. I'd recommend you don't use the AWS Linux build though - use the Ubuntu one.

You find the login.tpl in the plugin folder of the theme you are using, e.g. /node_modules/nodebb-theme-harmony/templates/login.tpl After changing a template you have to rebuild & restart your nodebb to see effects.