How to make visible all years in the availability calendar

In order to show all years in the availability calendar you should navigate to Menu Appearance => Editor, find file page-calendar.php and paste this string

<?php availability_dropdown(); ?>

after next code:

<div id="content-wrap" class="container"> 
<div class="breadcrumb"> 
<div><h3><?php the_title(); ?></h3></div>
<div><?php ggt_breadcrumbs(); ?></div> 
</div> 
<?php if (is_left_sidebar()): ?> <div class="col-lg-3 col-md-3 col-sm-12"> 
<?php generated_dynamic_sidebar(); ?> </div>
<?php endif; ?>

So you will get this code.

And this is result.