Click cell C6 in the Data worksheet and insert a column. Type Series Name in cell C6. Click cell C7 in the Data worksheet and insert a lookup function that identifies the series code, compares it to the series legend, and then returns the name of the series. Copy the function you entered from cell C7 to the range C8:C22. Change the width of column C to 18.

I was able to obtain an image of the "Data Worksheet" referenced (attached).

First we click on the C6 cell, and click the "Insert column" toolbar button.

Then on the same cell we type the column name "Series Name"

On the cell below (C7) we'll type the VLOOKUP function as follows:

=VLOOKUP(B7;$A$2:$C$4;2)

FIrst argument (B7) is the term to search

Second argument ($A$2:$C$4) is the table containing the terms to search and the results to return.

Notice the use of $ to avoid errors while copying the formula.

The third argument (2) means the function will return the 2nd column from the "Series Legend" cells.

Finally we'll copy the formula in C7 and paste it to the cells below C8 to C22.

To resize the column just drag the right side on top of the column, mouse icon will change to a double-pointed arrow.