@BobHoy Thanks for reaching out!
Would it be possible for you to upload a picture of the part? That would make it much easier to identify what it was for. If needed, you can find instructions for uploading a photo to the community here.
@BobHoy Thanks for getting back to us with a picture!
Based on what we can see, it looks like this part is the 'banner', which fits across the back of the chairs. You can see it in use with the 5 person model in one of the photos from TravelChair's website, here. It appears that the banner can be used to block wind, create privacy, or can be imprinted with the logo or team name if the chair is being used for a sporting event.
Hope this helps!