Could you be a bit more specific about what you want. Just guessing now:
If you have a textbox control in your repeating table double click the control and under Data Type select Whole Number or Decimal.
If you want to have something like a counter in your repeating section just drag an expression box into it, click the fx button, select insert function and write position() as the function.
Not sure if that is what you were asking so just let us know if you need any help