How do you edit a blank table in dataflow?

John1,

Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("fZRBrsMwC.....", BinaryEncoding.Base64)

I can reproduce this. This kind of function will exist when you use "Enter Data" button in power bi desktop, however, it seems like dataflow doesn't allow user to change data they entered currently. I would suggest you to submit your idea here. As a workaround, you can create a blank query and use power query language below to generate or modify a table:

let
  Source = Table.FromRecords({  
            [CustomerID = 1, Name = "Bob", Phone = "123-4567"],  
            [CustomerID = 2, Name = "Jim", Phone = "987-6543"] ,  
            [CustomerID = 3, Name = "Paul", Phone = "543-7890"] ,  
            [CustomerID = 4, Name = "Ringo", Phone = "232-1550"]  
      })
in
  Source

Regards,

Jimmy Tao