You will need to create 2 other groups in your data source to store the second
and third contacts. Once you have the additional groups created go to the
repeating person group you should have created already, right click and select
reference. Once the window opens select  the second group you created. This will
add the same structure under the new group. Repeat this for the third group.
Then set your additional contact  selector to store data in the newly created
fields.