Dear Dominik,
Please check this page: http://wp-types.com/documentation/user-guides/repeating-fields/, especially item #4 – the index attribute.
For CRED, when you create a generic field of type Select, you can populate the options either by hand or even by using a View if you want.
Please let me know if you are satisfied with my answer and if I can help you with any other questions you might have.
Pozdrowienia,
Paweł