Hi,
As you have a custom product page layout, I can't say for sure as I don't know how your layout was customized by your template provider (or yourself ?).
However, it's likely that by changing the line:
$specif_tab_content = trim($this->loadTemplate()) . $specif_tab_content;
to:
$specif_tab_content = $specif_tab_content . trim($this->loadTemplate());
in the file product / show_tabular.php via the menu Display>Views, you'll be able to do that.
If that doesn't work, then it's hard to say precisely. You would first have to activate the "Display view files" setting of the HikaShop configuration to check which view file is used to display the product page layout and if you don't find that code in show_tabular, then you should check with your template provider.