Actually, WP Travel logo image will have appeared on a single trip page when no image has been uploaded as well as has been selected as the featured image for the trip.
So, if you are willing to change the WP Travel logo image then you have to add the image through the gallery section and make it featured by clicking the image(the yellow star will appear in the image when it will be featured) for the trip.
You can add images for the trip by going to Admin Panel > Trips > Individual Trip(edited) > Gallery.
For detail assistance regarding adding images and making images featured, please refer screen record.
Further, if you have any queries, please submit them to our Contact page.