You can set this by inserting this CSS code in Custom wpDataTables CSS under the “Custom JS AND CSS” in main settings of wpdatatables.

@media screen and (min-width: 780px) {
   .wpDataTablesWrapper div.wdtscroll {
     overflow-x: initial !important;
   }
}

This will be affected on all tables, but if you want just for specific one then insert this code on page where is that table between the style tag.(<style>Code here</style>)

<style>
@media screen and (min-width: 780px) {
    .wpDataTablesWrapper div.wdtscroll {
      overflow-x: initial !important;
    }
}
</style>

Please note that Scrollable option should be turned on in the table settings.