Change the values of the report header text box dynamically based on the page content.

Sometimes the report header needs to change from page to page. For example, on page one, the vendor ID and description must be displayed, and on page two, the vendor ID and description for a different vendor must be displayed, as shown in the screenshot below.

This is simple to achieve with a table, but header does not support tables. You can only create a textbox in the header.

To accomplish this customization, data must first be organized in the Tablix. The data in the Tablix must be grouped, and a page break must be added at the end of each group.

To set page break to a row group:

• In the Grouping pane, right-click a row group, and the click Group properties.
• On the Page Breaks tab, Select Between each instance of a group and Also at the end of a group to specify that a page break be added when group ends in the table.

This will group vendor records related to each vendor ID into their own page.

Add the fields that need to be displayed on the header in a separate row within the group in Tablix, as shown in the screenshot below.

Set row visibility to hide to ensure that this field does not appear when printing the report. Make a note of the field name from the properties. Assume the name of the field is textbox1. Create a text box for the vendor id in the header. Enter =ReportItems!textbox1.value in the text box expression.

Keyword Reportitems returns a list of all the fields in the report. Textbox1.value returns the textbox1's current value.

https://learn.microsoft.com/en-us/sql