Excel and Power Query are too different to allow for something like a button that would convert Excel formulas to Power Query code.
Probably it is not a good idea to have the data in the Excel sheets moved into Power Query without first making a redesign of the data structure: typically Excel data is organized in flat files (sheets and or tables), while Power Query structures data into a data model.
My approach would be to design the data model and then create the code in Power Query (using the available menu options and/or manually in the formula bar / advanced editor) to get the data into the data model.
Probably I would use an overview of the formulas used in the Excel sheets (either via tab FORMULAS - Show Formulas OR via a separate overview using Excel function FORMULATEXT).