Move the quantity button in product page

Hi,

If you turn on temporarily the "Display view files" setting of the HikaShop configuration, you'll see exactly which view file is used to display which area. Then, you can just edit the view file via the menu Display>Views.
For the quantity input field, that's likely the file "quantity.php" of the view "layouts" that you want to edit.
Note that the quantity input field can be displayed in different ways thanks to the "Quantity input method" setting of the HikaShop configuration.
I would first recommend to choose the display method you want for it in that setting, before customizing its HTML in the view file. That should save you some time.