Notice the scrollbar next to the field where you chose “ASIN”. You must have a really small screen (or perhaps the window size is scaled small), because Airtable isn’t able to display all of the necessary fields. Once you chose the first field option, a second field choice appears. However, in your case, you’ll have to scroll within that dialog to see it. That second field is where you choose the field in the target table that you want to roll up. After that a third field will appear (probably requiring more scrolling for you) where you enter an aggregation function to apply to the rolled-up data.
