Two good resources philio.me novoda
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<item name="searchViewStyle">@style/AppTheme.SearchView</item>
</style>
<style name="AppTheme.SearchView" parent="Widget.AppCompat.SearchView">
<item name="searchIcon">@drawable/ic_action_search</item>
<item name="closeIcon">@drawable/ic_action_close</item>
</style>
mSearchView = (SearchView) searchViewMenuItem.getActionView();
int searchImgId = getResources().getIdentifier("android:id/search_button", null, null);
ImageView v = (ImageView) mSearchView.findViewById(searchImgId);
v.setImageResource(R.drawable.your_new_icon);