I read the question again and I add a disclaimer here. If this is what you want 
All you need is a custom state called Start (or whatever you want) and the repeating group will show the data starting from that number. Then, the arrows will just increase and decrease these numbers. See demo below:
Repeating group has this data source, starting from custom state:
And the left arrow for example, just decreases the custom state:
And vice-versa for the right arrow. You can put some limits so they don’t go above and beyond the size.
Here is the editor if you want to check details: Tests for Forum 11 | Bubble Editor