If you want to correct the thumbnail close the menu and reopen it again when you're ready. The picture for the thumbnail is taken from your point of view when you press a 'Open DupePublish menu' button.
In the publish menu there's a thumbnail preview. There, at the top of the window you'll find a button for opening the Publish menu but before that I encourage you to read the rules and tips. To upload a duplication go into the 'Publish & Readme' tab. If you have Advanced Duplicator 2 installed it will automatically switch to the toolgun and update current dupe, so you'll be ready to paste it in no time! There you can click a green down arrow to download a duplication file. To browse dupes go into the 'Browse tab'. How to useGo to the Spawn menu (press Q), open the 'AdvDupe Share' tab.