To do this, create a group in a data region, add a page break to the group, and then add a group expression to group by a specified number of rows.
The below expression, when set as the group expression, assigns a number to each set of 50 rows. When a page break is defined for the group, this expression results in a page break every 50 rows.
=Int((RowNumber(Nothing)-1)/50)
For more details refer the link below :
Report Expressions[
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Hope this helps.