Tablix Group Properties Dialog Box, General
Select General on the Tablix Group Properties dialog box to change name, group, and page break options for the group.
Type a case-sensitive name that begins with a letter and has no spaces. The name can include letters, numbers, or underscores (_). The name must be unique in the report. By default, a general name based on the group expression, such as OrderDate or SalesPerson, is assigned.
Add a new group to the data region.
Delete the selected group.
Choose the field or expression on which to group the data. Click the Expression (fx) button to edit the expression.
Type the next field or expression on which to group the data. Click the Expression (fx) button to edit the expression.