To override a template file, we simply copy it from the default theme to our custom theme.
In this example we'll change the search field, as seen below.
So let's copy this file:
And paste it into our theme:
Inside the file let's remove the 'Magnifying Glass' code below.
<span class="fa fa-search" title="<?php echo $lang_title_search_icon; ?>"></span>
And the final result: