Are you saying that you want to check whether an entry in column B is also present in Column A, and if so - then write the value of the information in Column C to the Account ID column?
If so, then it should be simple:
In column D
=If(isna(vlookup(B2,$A$2:$A$100,1,false)),"",C2)
where A2:A100 is the length of the list. Then just copy the formula from Cell D2 to Cell D100
I am sure that other people can improve on the formula, but this gives you the principle.