Hello,
Ok, you have to create an override view of your view (show_default, show_reversed or show_tabular, depends from your product page configuration).
See this tutorial to see how to proceed,
here
.
You have to look for "$this->element->extraData->bottomMiddle" or "$this->element->extraData->bottomEnd" (so far I don't know which display your custom Item), then copy paste the whole line like show on my screenshot :
Then, you have to look for the code part that manage your "
Add to cart" button, for this look for "
hikashop_product_quantity_main" and paste the previous code part
Hope this will help you achieved your needs.
Regards