Hi, 

You can set the flow in the following fashion.

        the automated action will get triggered when the approval request goes from submitted to the approved stage. 

    2.    Second created an Email template and  in the to part you can use jinja2 to extract the created by field of the approval request. The following snippet will give you an idea about what I am saying.

If followed the above two parts correctly, you'd be able to get the functionality you want. If not then please comment.

Thanks and Regards,

Divyansh