How can a TextBox show a collection of fields?!
TextBox can only show one field if it binds to a collection.
But you could plan for another property like "SelectedField" that is not a collection and bind the TextBoxes to it.
If you want to load the previous data that you have saved. Then Create a table in database (for Example: DataLog):
This table must relate to the main data table (1 to 1) ID to ID
If you have only one User then Ignore User_ID
Ok you can query for the last Data that the user has entered. on OnLoad or every time.
var data = MyDataCollection.OrderByDescending(d=>(d.DataLog.SavedDateTime && d.DataLog.User_ID == myID));
var selectedData = data.First();