I have generally done this in the past by targeting the link that adds a row and triggering its click action.
$('[data-key="your repeater key here"] .acf-actions a.add-row').trigger('click');
Then adding an append action https://www.advancedcustomfields.com/resources/javascript-api/#actions-append to populate the sub field using the fields set method https://www.advancedcustomfields.com/resources/javascript-api/#functions-set