From: https://msdn.microsoft.com/en-us/library/dd207045.aspx

  1. On the design surface, click the row or column handle of the tablix data region to select it. The Grouping pane displays the row and column groups.

  2. On the right side of the Grouping pane, click the down arrow, and then click Advanced Mode. The Row Groups pane displays the hierarchical static and dynamic members for the row groups hierarchy and the Column groups pane shows a similar display for the column groups hierarchy.

  3. Click the static member that corresponds to the static member (row or column) that you want to remain visible while scrolling. The Properties pane displays the Tablix Member properties.

    If you don’t see the Properties pane, click the View tab at the top of the Report Builder window and then click Properties.

  4. In the Properties pane, set RepeatOnNewPage to True.

  5. Set KeepWithGroup to After.

  6. Repeat this for as many adjacent members as you want to repeat.

  7. Preview the report.