If you made changes to MyobCsvMaps.xml before the upgrade, MYOB will back up this file to the folder <MYOB directory>\CENTRAL\Deploy\Client Accounting Templates.
You can open this file and manually copy over any custom mappings to a new Map in the MyobCsvMaps-User.xml file, which is located in the folder indicated in the table above.
After you have copied your changes, you may delete MyobCsvMaps.xml if you wish. Any future updates should be made in MyobCsvMaps-User.xml.