How to use custom search icon (what to link it to?)

Hi, I am using the Magazino theme on my WP site and my question is how do I update the header.php file to use a custom link/icon for my search button? Right now the search button is being called by <div id="search-icon"></div> but what if I want to use my own image? Is there an easy way I can hook the search box to appear when clicking on a link? How would I do that? Thank you!