Hello, @Shehzad Ghazi,
In order to solve your issue simply go to the Dashboard >> XStore >> Theme OPtions >> Theme Custom CSS >> Global and then paste the below code at the bottom of the CSS box there.
.page-id-20 .product-stock.step-1 span.stock-out{display:none !important;}
.page-id-20 .product-stock.step-1 .stock-in{width:100% !important;}
Then save settings and check back to your site after clearing the browser cache.
The result will appear like this: https://postimg.cc/QFbDJJJM
Regards 8Themes Team.