Main image not showing in thumbnails? Dawn theme

[Frankfurt]

Hi I have added some code so that only the selected variant images show.  The problem is that when I click on a thumbnail so that it takes the place of the main image, I can't get back to the main image as it is not showing in the thumbnails. I tried just adding the main image to the product a second time which worked ok on desktop but on mobile it means the same image appears twice directly after each other on the slider? Any ideas how to either get the main image to automatically be included in the thumbnails on desktop or to remove it (or the second image) just from the slider on mobile view?