Reset the export settings
There are a lot of settings in the Export Artboard dialog. If for some reason you want to start over and set everything to normal you can use the reset button.
Any options you have set will be lost and be reverted to default.
As with any change to your document in Adobe XD any action through a plugin you can undo or redo. So if you didn't mean to reset the document you can "Undo" that action in XD.
You can view the artboard preferences by clicking on the artboard name in the top of the screen.
That shows these details: