How can I change the thumbnail of my item photo?
To find the items you listed, go to Marketplace and then click on that navigation on My Items.Here you can find a list of all the items you listed.You can Edit/Manage or Delete your items here.Click on Edit and find the edit items tool box:
Here click on Edit Item Photo.Here you can set a new Thumbnail. Click on Edit Thumbnail by move the small field in the picture to where you want it, then click on Save Photo: