Full solution can found here: https://www.elegantthemes.com/forum/viewtopic.php?f=187&t=446328&p=2477902#p2477902

swap-column-order.css

@media only screen and (max-width: 980px) {
    .fix.et_pb_row {
        display: -webkit-box;
        display: -moz-box;
        display: -ms-flexbox;
        display: -webkit-flex;
        display: flex;
        -webkit-box-orient: vertical;
        -moz-box-orient: vertical;
        -webkit-flex-direction: column;
        -ms-flex-direction: column;
        flex-direction: column;
        /* optional */
        -webkit-box-align: start;
        -moz-box-align: start;
        -ms-flex-align: start;
        -webkit-align-items: flex-start;
        align-items: flex-start;
     }
    .fix.et_pb_row .left.et_pb_column.et_pb_column_1_2 {
        -webkit-box-ordinal-group: 2;
        -moz-box-ordinal-group: 2;
        -ms-flex-order: 2;
        -webkit-order: 2;
        order: 2;
     }
    .fix.et_pb_row .right.et_pb_column.et_pb_column_1_2 { 
        -webkit-box-ordinal-group: 1;
        -moz-box-ordinal-group: 1;
        -ms-flex-order: 1;
        -webkit-order: 1;
        order: 1;
     }
}