|Since we can't see your spreadsheet from where we're sitting, we can only make assumptions and make suggestions based on that.|
If your spreadsheet looks something like the table below, then VLOOKUP might work for you.
A B C
1 Some Data Emp Number A More Data
2 Some Data Emp Number B More Data
3 Some Data Emp Number C More Data
4 Some Data Emp Number B More Data
Create a table with Client Numbers and their associated Names.:
1 Emp Number A Bob
2 Emp Number B Steve
3 Emp Number C Sue
Next in F1, enter this and drag it down:
=VLOOKUP(B1, $D$1:$E$3, 2, 0)
This will lookup the Emp Numbers from Column B and return the value (the name) from Column E.
(Review the Excel Help files for VLOOKUP to see how it works)
Once you have a list of Names in Column F for all the Emp Numbers in Column B, copy those names and do a Edit...PasteSpecial...Values over the Emp Numbers in Column B.
This will paste the values (the Names) not the formulas. It will also return a bunch of #N/A in Column F, but you shouldn't care because you don't need that list any more. Just delete anything you don't need.