It's not possible to append a row to an ACF repeater field without a custom code workaround that utilizes our API: http://www.wpallimport.com/documentation/developers/action-reference/.
The following is an example to show you how this can be done. You will almost certainly need to adjust the code snippet to make it work with your data/site.
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Create a new "Manual Record Matching" import that updates the post(s): http://www.wpallimport.com/documentation/recurring/manual-record-matching/
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Store the ACF data in your own dummy custom field: http://d.pr/i/3Si4ad.