For items to be sorted by aisle, you must be in the In-Store shopping mode. If your items are sorted by department, it means that you are in Curbside or Delivery mode.
If you are viewing your list in In-Store shopping mode, you can sort your list by clicking on the List icon in the upper right-hand corner of your screen. This will bring you to a page titled “Review List”.  Select “Sort List” at the top of your page and choose to either sort your list by aisle or sort by department.