Hello, @KD,
Thanks for the screenshot I have understood your issue.
Now, in order to solve your issue simply go to the Dashboard >> XStore >> Theme Options >> Theme Custom CSS >> Global and paste the below code at the bottom of the CSS box there.
@media(max-width:767px){.woocommerce-tabs.horizontal .wc-tabs{
width:100% !important;
display:block !important;
white-space:initial !important;}}
Then save settings and check back to your site after clearing the browser cache. The result will appear like this: https://postimg.cc/pywX3tRZ
Regards 8Themes Team.