To use Source Data to migrate data
The starting cell in the Target Range must be one row below where you have your fields mapped. So if you have all fields mapped in A3:J3 for example, the Target Range would be A4.
The Paste from mapping function in runtime will copy all data in the list range from the source based on the source range starting location. For example, if you have a data range from A3:J3, it will copy all cells in that range into the target App.