I think this article will be useful for you >>>  

The above article is good for learning how to parse the XML contained by a repeating section. If you want to have the data in a separate child list in SharePoint I suggest the TekDog controls. http://www.tekdoginc.com/nintex-form-controls 

Repeating table data is stored as XML. Set the table to a multi-line plain text field, put in a loop, then use the query XML action to extract the values from the rows

@zakaria_botros - here is a blog showing how this can be done. The concept is the same in both on-prem and o365 https://community.nintex.com/t5/Community-Blogs/How-to-get-data-from-a-form-repeating-section-in-O365/ba-p/89490. You can also view https://community.nintex.com/t5/Template-Gallery/Parsing-Nintex-Forms-Repeating-Section-Solution-O365/ta-p/85704 for help as well.

This doesn't solve the issue. The linked article's images are too low quality to be useful. The attached example ZIP files when renamed to NWF and imported throw an error.