This help page has a nice write up for the defaultconfiguration.xml. If you do not have a default .xml editor on your system, you can save the file, change it in notepad and upload it back to the document library. Then rename the original and change your new file to the defaultconfiguration.xml
[INDENT][/INDENT]Thank you for your reply . I've tried to change the configuration xml like the following . However I got error message (JSON Error....). The help page do have an example showing how to change the basemap to ArcGIS tiled service . But I want to change it to Bing map . Would you give me some further advice ? Thanks .