When you first subscribe to A2X, approximately 10 settlements will come into your settlements list automatically. To retrieve settlement history older than what A2X automatically imports, go to Settings > History. Click on Request More History:
It is helpful to check Amazon to make sure the settlements are available and not archived. See this article on how to check:
Why are some of my settlement files missing in A2X?
Please wait for up to 12 hours after requesting history to confirm all missing settlements have imported.