Thanks for reaching out. If I understood correctly, you are looking to export a specific area of an image? If yes, we do have an option to export a specifically selected asset however we don't have the option to export a specific area of that asset. As a workaround, you can try creating a path around that specific area using the Pen tool, and then you can try exporting it. For more information on export options, please refer to this article: https://helpx.adobe.com/xd/user-guide.html/xd/help/export-design-assets.ug.html
This may not be feasible in all the workflows so do let us know if this helps or if you need any further assistance.