Join all sheets in one excel after transforming them individually

hi, snaise 

1. Create a custom function with all your transformations steps.

2. Read your file with Excel.Workbook(File.Contents("C:\Book1.xlsx"), null, true)

3. Filter [Kind] column to get sheets only. 

4. Apply your function to [Data] column: Table.TransformColumns(Source, each {"Data", my_function})

5. Table.Combine [Data] column

So 

let
    Source = Excel.Workbook(File.Contents("C:\Book1.xlsx"), null, true),
    filter_sheets = Table.SelectRows(Source, each ([Kind] = "Sheet")),
    my_function = (t as table) =>
        let 
            a = Table.RemoveFirstN(t, 3),
            b = Table.PromoteHeaders(a),
            c = Table.RemoveFirstN(b, 1),
            d = Table.UnpivotOtherColumns(c, {"Column1"}, "Attribute", "Value")
        in d,
    transform = Table.TransformColumns(filter_sheets, {"Data", my_function}),
    combine = Table.Combine(transform[Data])
in
    combine