Select Sorting on the Tablix Group Properties dialog box to specify a sort order for the unique values for this group. For the default details group, this specifies the sort order for all the data rows.
Add a new sort clause to the list.
Delete a selected sort clause.
Move the selected sort clause up in the list.
Move the selected sort clause down in the list.
Select the field on which you want to sort, or enter an expression to specify the sort order
Choose A to Z if you want to sort from the lowest to highest; for example, from 1 to 100. Choose Z to A if you want to sort from the highest to the lowest; for example, from 100 to 1.