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