Hello @Parag
The quantity is set to 1 value by default and it can be changes when the quantity select is displayed across the product content. We provide next options in our Archive Products widget -> https://prnt.sc/S8z4wft_QZvB and the work of such configuration can be usefull for your case as it adds 50 amount at once. Please, check the work of add to cart button now as we set the correct settings on your web-site.
Kind regards, Jack Richardson
The 8theme’s team