let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Changed Type1" = Table.TransformColumnTypes(Source,{{"Salaries & Wages", type text}}),
#"Demoted Headers" = Table.DemoteHeaders(#"Changed Type1"),
#"Added Custom" = Table.AddColumn(#"Demoted Headers", "Custom", each if Text.Contains([Column1],"Salaries") then [Column1] else null),
#"Filled Down" = Table.FillDown(#"Added Custom",{"Custom"}),
#"Filtered Rows" = Table.SelectRows(#"Filled Down", each ([Column1] <> "Salaries & Wages")),
#"Reordered Columns" = Table.ReorderColumns(#"Filtered Rows",{"Custom", "Column1", "Column2"})
in
#"Reordered Columns"

As a variant and assuming you want to apply this not only to areas in the table (referring to the screenshot) where the header contains the word "Salaries".

let
Source = Excel.CurrentWorkbook(){[Name="myData"]}[Content],
#"Added Custom" = Table.AddColumn(Source, "Custom", each if [Column2] is null then [Column1] else null),
#"Filled Down" = Table.FillDown(#"Added Custom",{"Custom"}),
#"Filtered Rows" = Table.SelectRows(#"Filled Down", each ([Column2] <> null)),
#"Reordered Columns" = Table.ReorderColumns(#"Filtered Rows",{"Custom", "Column1", "Column2"})
in
#"Reordered Columns"

Hi Alan, First of all thank you for your response but I think I have not done a good job explaining this.  It is not only Salaries and Wages it will contain many other expense and revenue categories.  Please see below.  I do apologize but I am super new in PowerQuery and probablyl my lack of experience is hindering my exlanation and what you need.  Can I provide more information somehow to make my help request better?

Riny, I placed the formula in but it says it cannot find the excel table.  I tried both MyData nd PS Detailed.  I think maybe it is how I am pulling in the table perhaps.  I added the screnshot so maybe it can offer some clues.  It is a connection to an SQL Server, in the database name PMReporting_Work and it its grabbing table PS Detailed.  Sorry guys I am just so new this and I am probablly frustrating some people.  I hope to get better at PowerQuery.

Expression.Error: We couldn't find an Excel table named 'MyData'. 

OR

Expression.Error: We couldn't find an Excel table named 'PS Detailed'.

The Source step and Column names used in the query are subject to your own data structure. It it's a structured table, use the correct table name. In my example I used a named range called myData (with a small m) and without headers. So it landed in PQ with two columns called Column1 and Column2.

So, just connect to the source as you normally would and when you get to the point that you want to add the custom column, make sure that the #"Added Custom" step is referring to the correct column names, whatever these are at this point in the query.

You can follow it step-by-step in the file I uploaded with my first answer.

Hi Riny,

I am sorry but I just cannot get it to work.  It must be something trivial that I am missing.

I think I fixed the connection to the table issue by adjusting as follows but now I am getting an error saying that the subaccount column was not found. 

let
Source = Sql.Database("vwp-fi-", "PMReporting_Work"),
#"dbo_PS Detailed" = Source{[Schema="dbo",Item="PS Detailed"]}[Data],
#"Added Custom" = Table.AddColumn(Source, "Custom", each if [Subaccount Description] is null then [Subaccount] else null),
#"Filled Down" = Table.FillDown(#"Added Custom",{"Custom"}),
#"Filtered Rows" = Table.SelectRows(#"Filled Down", each ([Line_Description_Desc] <> null)),
#"Reordered Columns" = Table.ReorderColumns(#"Filtered Rows",{"Custom", "Subaccount", "Subaccount Description"})
in
#"Reordered Columns"

Sorry I am doing my best I just cant seemt o figure it out.  I changed the two column names so its easier to distinguish.  I tried to put in as much detail for you to see and hopefully it is something you can spot off the bat.

Thank you for your patientce with me.

I can't really relate the error message to the script you copied into your message, but are you sure that the column name is really "Subaccount" at this stage? Two steps down you refer to [Line_Description_Desc] which, based on your first message seems to contain what you now refer to as [Subaccount]. Make sure that the column names are indeed as included in the previous step. Attaching a file with my mockup that looks a bit like yours now.

@riny Hello Riny, I'm trying to use the technique you explained in your answer to this question. I can't see the file you attached and referred to here, which I think would help me a lot to understand how to use the LET function (I'm very much a beginner with PQ).Any chance you could re-attach the file? Many thanks.

@julian8759 After the migration to new forum software a while ago, file attachments did not migrate with the questions and answers. And I have cleaned-up all my old files from before 2023.

But perhaps better you start your own question and attach your own example data. The you'll get an answer that specifically addresses your situation. 

Thank you Riny. I persisted and experimented with your solution, and was finally able to make it work for my specific need. And learnt a few things about PQ along the way! Thanks again.