How do I set 1st row value from sql script in ssrs report?

I'm working on SSRS report.

There are two main fields CurrentMV and PreviousMV both are having there different formulas but I'm taking PreviousMV as a value of CurrentMV using =Previous(Sum(Fields!CurrentMV.Value))

Now How can I set 1st field only from sql and rest of other as it is coming from expression?

Because of I'm using Previous function 1st value is always coming null :(

I have the field in reporting proc which can give me the values but How can I set both 1st values as well as Previous function ?