Navigation function

Hi,
I have the cumico theme and I want to edit the header navigation cause I want to add some socials icons there.
The problem is that watching the code of header.php, I found that:

<div id="master-wrapper" class="<?php echo ''.$layout_style.' '.$layout_width.'' ?>">

	<?php st_above_header();st_header();st_below_header();?>

but I don’t know where to find the st_above_header(), st_header(), st_below_header(). In which file and folder are they? I need to find that to see where I can change the code to add some code by myself.
Thank you,

Gemma