Conditional Renamed Columns

let
Source = Table.Combine({#"tempAmb(DateStart)",#"tempAmb(DateEnd)"}),

- Here, i want to check if there is a column with the name:"firstName"

#"Renamed Columns" = Table.RenameColumns(Source,{{"firstName", "secondName"}})
in
#"Renamed Columns"

So, if the query has a column called "firstName" it will be call "secondName" at the end.

I'll hope that this example would be enough to understand the problem, if not, I can write pseudocode PattemManohar 

Thanks 

aoliver  You can try unpivoting the columns and then replace the values under Attribute field from FirstName to SecondName, then finally pivot the table again.