Change Data Source from offline excel to SharePoint

If you go into 'Transform data' and look in the advanced editor for your query it will look something like this for local files...

// Local        
let
  Source = Excel.Workbook(File.Contents("D:\Downloads\book.xlsx"), null, true),
  Sheet1_Sheet = Source{[Item = "Sheet1", Kind = "Sheet"]}[Data],
  #"Promoted Headers" = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars = true]),
  #"Changed Type" = Table.TransformColumnTypes(
    #"Promoted Headers",
    {{"a", Int64.Type}, {"b", Int64.Type}, {"c", Int64.Type}}
  )
in
  #"Changed Type"

What you need for SharePoint is something that looks like...

// SharePoint             
let
  Source = SharePoint.Files(
    "https://youdomain.sharepoint.com/sites/yoursite",
    [ApiVersion = 15]
  ),
  #"Filtered Rows" = Table.SelectRows(Source, each ([Name] = "book.xlsx")),
  ExcelFile = #"Filtered Rows"
    {
      [
        Name = "book.xlsx",
        #"Folder Path"
          = "https://yourdomain.sharepoint.com/sites/yoursite/Shared Documents/Data/"
      ]
    }
    [Content],
  #"Imported Excel Workbook" = Excel.Workbook(ExcelFile),
  Sheet1_Sheet = #"Imported Excel Workbook"{[Item = "Sheet1", Kind = "Sheet"]}[Data],
  #"Promoted Headers" = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars = true]),
  #"Changed Type" = Table.TransformColumnTypes(
    #"Promoted Headers",
    {{"a", Int64.Type}, {"b", Int64.Type}, {"c", Int64.Type}}
  )
in
  #"Changed Type"

Essentially, you need to replace the top row of the local one with the top couple of rows of the SharePoint one. Obviously that varies depending on the complexity of your setup.

Hope that helps.