If you are trying to import FBA orders the site navigation is as follows: Seller Central > Reports > Fulfillment > Amazon Fulfilled Shipments > Request .txt Download
At this step, the contents of the file will be displayed to you. So, you will see all orders in the file, even if those orders are already in AOB, but Don't Panic because the normal operation of AOB compares incoming Order IDs against existing account data. Any Order ID that already exists in your AOB account will be ignored.
Looking at your AOB Ship page:
It is important to note here that orders which have been confirmed on Amazon prior to being imported to AOB should not be confirmed to Amazon again. Amazon's frown at this behavior is large and frightening. To avoid doing so use the Move to Previously Processed option in the Actions column of your Ship page.
Also if your order has been canceled already on Amazon use the Move to History option in that same section.
These actions will clear up your ship page so that all you have left are orders that need to be confirmed as per your usual operations.
While I have likely left out some bit of information feel free to Sign In to your Help Center if you are not already by using the Sign In button at the top right of this page ... ... as doing so will allow you to interact and leave comments that I can address directly on this page. Adding comments here will also allow others to benefit from the knowledge.
Lastly, while the creation of this page was an effort to workaround an excruciating glitch in the connection with Amazon order feeds it has been decided that the page will be kept active as we see the potential for its use in a variety of situations.