//Copy flatsome theme file to child theme and add below code code to it.
themes/flatsome/woocommerce/cart/cart.php

Search this line  <div class="col large-7 pb-0 <?php echo $main_classes; ?>">
and replace it with  <div class="col large-12 pb-0 <?php echo $main_classes; ?>">


Search this line <div class="cart-collaterals large-5 col pb-0">
add replace it with below code
<div class="cart-collaterals large-7 col pb-0"><h2>My Custom stuff will be there</h2></div>
<div class="cart-collaterals large-5 col pb-0">