This is not possible with the default XLSReport / Excel Exporter module from the AppStore. Most users are probably able to create charts in Excel themselves, so only follow down below road if really needed:
In my Word Exporter module from the AppStore you can add basic Excel charts; column/bar and line. If you need to extend this functionality to an Excel export, you need to adjust the 'XLSReport / Excel Exporter’ AppStore module via Java. You can use my Word Exporter project to see how this could be achieved. It is not beginner level, though and needs some understanding of the Apache POI library.
You could add an excel file template to your export. You can set up a blank sheet where your data is going to be filled in and a second tab in your file which uses the data to show a graph.