Hi,
Follow the below steps to achieve your requirement.
1. Go to list box properties.
2. Select ‘Look up values in the form's data source' option in List box entries.
3. Select the first repeating table field (RT1F1) in the Entries box.
4. Add a text box below the list box.
5. Go to that text box properties.
6. Click on fx button beside the default value box. Select the list box field in that and click ok until the windows gets closed.