Solved
To my knowledge you can only change this image if you make a copy of the LandingPageAccessAppMashup and change the master of the copied landing page.

You can make a copy/dublicate of the original master "PTC.AccessApp.Master" and change this master to your wishes.
Insert the newly copied and modified mastermashup into copied LandingPage Mashup master.
Then bookmark the copied LandingPageMashup instead of the PTC OOTB mashup.
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