go to customize > additional css copy and paste  below css and published it 

.col-1 {
flex: 0 0 100%!important; max-width: 100%!important;}
.woocommerce .col2-set .col-2, .woocommerce-page .col2-set .col-2 
{ float: left; width: 100%;}
.col-2 {

flex: 0 0 100%!important;  max-width: 100%!important;  }