Hey @stevewesson
Not much idea about this. Nor I have used forms with csv files.
But I can suggest you some things.
Make use of file content if available.
If not save it to a place where you want to save it to. After that give some delay. Then after that start a child flow. Child Flow will access the content of the file. Then just take the values from that csv file and update it in your list.
You can also try it without child flow too, just give a delay so that the file is uploaded where you intend it to.
Then use appropriate action to get the file content of the file.
File content is the key here.