To eliminate potential double entry of Grade Center data, you can perform offline grading, and then import grades into Grade Center. You can also upload grades from external sources such as an Excel spreadsheet or a comma separated values (CSV) file. Data must be formatted very specifically to upload correctly and be synchronized with existing Grade Center data.
To learn how to download your grade book, edit it in excel, and upload the changes back to blackboard, please visit this link:
Uploading or Downloading Grade Center Items for Working Offline