Add column to data set using append

When you combine files, it takes a sample file that you pick, usually the first file. If that file doesn't have that column, it won't bring it in by default.

You can fix that though. Honestly, unless you are pretty good with Power Query, it might be easire to redo the Combine operation and pick the 3rd file vs the 1st file as the sample.

You can do it manually though by changing the index number of the sample file shown below. Change the {0} to {2} (it indexes at zero, then look at the Transform Sample File operation, and the other steps it created in your main query so it doesn't wind up removing the column after it brings it in.