If you have done your clients' measurements as an individual assessments but you need to create a group report afterwards, you can use the Group reporting tool. Actual group assessment can't be created from individual assessments because that creates a completely new assessments for all the participants.
Group report can be created like this:
1. Open Group reporting tool by selecting Tools > Group reporting tool.
2. Select New Group report from the low right corner of the view.
3. From the opening dialog select individuals or groups you want to add (Add individuals/Add groups).
4. Select the profiles or groups you would like to add to the group report and click Create reports.
5. Next set the report settings and click Create reports.
6. Created reports can be found from the list. When you want to open or edit the reports, select Open or Edit button from the same row than the report.
More information about the Group reporting tool can be found from the User guide.