1. Get the submitted forms out
Each submitted form is an .xml file in the form library. Select them all in the library and choose Download (you get a .zip), or Sync the library with OneDrive for big ones. Step by step here.
2. Flatten them to one CSV
A SharePoint list wants rows and columns. Drop the .zip into the InfoPath to Excel converter: it reads every form in your browser and writes one CSV, a row per form and a column per field, with the same columns for every form even when some left fields out. The first column records which .xml file each row came from, so you can always trace a row back.
Repeating tables (expense lines, order items) are joined into one cell by default, like "Hotel; Taxi". That fits a single list column. If the new design keeps them as a separate child list, choose "one column per entry" instead and split them out in Excel.
3a. Create a new list from the CSV
In SharePoint, New, List, From CSV, and choose the file. SharePoint suggests a column type for each column; check the dates and numbers before you click Create. This is the quickest route when the new list doesn't exist yet.
3b. Or fill a list you've already built
If the new list and its Power Apps form are already built, open the CSV in Excel, rename the column headers to match the list's columns, and paste the rows into the list's grid view (Edit in grid view). For thousands of rows, a Power Automate flow or a migration tool is steadier than pasting.
Things to check
- People fields: InfoPath stores names or account names as text. A list Person column needs a real user, so keep the old value in a text column if the person has left.
- Attachments: files attached inside a form are stored in the .xml itself. The CSV lists them by size; keep the original .xml files if you need them.
- Several templates in one library: convert each template's forms separately so the columns line up.
Up to 25 forms convert free. A whole library is $49 once, with a full refund within 30 days if it doesn't work for your forms.