SSRS Report: Lookup the nth row field value from a dataset

You can add a new column in your dataset to identifier the RowNumber of each dataset row, and then you can take use of the lookup function in Reporting services to retrieve the relevant value using RowNumber.

Eg:

RowNumber	Col1	Col2	Col3
Row1	11	12	13
Row2	21	22	23
Row3	31	32	33

You can use the expression below to retrieve the yellow highlight cell value:
=LookUp(“Row2”,Fields!RowNumber.Value,”DataSet_Name”)

Remember to replace DataSet_Name to your real dataset name.