How to mapping and return target data ?

I have 2 matrix:

A=IndivCellof1000customers_Export and

B=DayTpe

I try to map A.Var2 and B.Var1, if they are same value

they should return B.Var2 into A.Var5 in the same row.

It look like vlookup function in excel,

I try to use this code

if A.Var2==B.Var1
   A.Var5=B.Var2;
end

but I face a problem with this error "Data inputs must be the same size, or any of them can be a scalar."

How can I fix it ?

thank you in advance