Do you use SharePoint Online, or on-prem? InfoPath doesn't have anything out of the box for this, I'm afraid. There are third party tools you can use (qRules, FormsViewer), you can use custom code, and I know some people have used SSIS for this (getting the repeating data from the XML and then pushing it to a list on a schedule). If you are using SharePoint Online, you can't use qRules, code, or CAML - so you'd need to either find a way to get the data from the XML with a tool like SSIS or possibly MS Flow, or you could use FormsViewer which has this capability built in. If you are using SharePoint on-prem, you may be able to write custom code, or use qRules or even CAML (there are a couple long posts on this forum about how to use CAML for this). Hope this helps - sorry this is so complicated - it seems like one of those things that should have existed out of the box. :)
Hilary Stoupa
