To bulk-enroll students into groups, the groups must be created first. If you only need a few groups, the easiest option is to create them manually.
If you need a large number of groups, use the instructions in the following article: How do I create groups in bulk for group assignments?

Once you have created the groups in your course, it’s best to use the Use the Group Management Widget to populate the groups.
Click Download Classlist in the Group Management Widget on the homepage.

The file you downloaded can be used later for importing. The file contains all the student data from the course. To make the file easier to work with, select column A and go to Data > Text to Columns.

Choose Delimited and click Next.

Select Comma and click Next.

Click Finish in the final step. The data will then be placed into separate columns, making it easier to fill the file with the student and group information.

The columns Username, GroupName, GroupCode, GroupCategoryName, and Action must be filled in for the file to be processed correctly.

The GroupName, GroupCode, and GroupCategoryName must match exactly with the information in Brightspace. You can find GroupName and GroupCode by clicking on a group.

The GroupCategoryName can be found under Manage Groups

For Action, enter ENROLL, and your file will look something like this.

Save the file via File > Save As. The file name must always start with classlist_, and it must be saved as CSV (Comma delimited) (*.csv).

After saving, close the file, locate it in the folder where you stored it, and then open the file with Notepad.

Next, press CTRL + H, enter ; (semicolon) in the first search field, , (comma) in the second search field, and click Replace All.

Then save the file again and close it.

Finally, go to the Course Homepage and import the file you just created into the Group Management Widget by clicking Browse Files or by dragging the file into the widget.

The file will be checked, and then you can click Import to process the file.

When the file is processed successfully, you will see the message All actions were successful.
If there are errors in the file, an error message will appear and a report will be downloaded showing the mistakes. You can then use this report to correct and reprocess the necessary rows.