1 - Add a file uploader.
2 - Add a repeating group with the datatype set to “file” and leave the data source empty.
3 - Create a workflow: When FileUploader’s value is changed.
4 - Add an action: Display list in a repeating group.
5 - Select the repeating group you created and set the data source to: Repeating Group File: plus item This FileUploader’s value.
Here is an example in the editor for you to see it in practice.