Hello Haolingoa,

To create an Excel file, you should used the library "xlwt".

In the first time you must created a "TransiantModel", in this model you create a "fields.Binary". This binary field will be your "Download link". 

class YourWizard(models.TransiantModel):
     _name = "your.wizard"
     
     your_excel = fields.Binary(string="Your excel")

     
After you generated your excel with library "xlwt" (Documentation; https://xlwt.readthedocs.io/en/latest/) or one other library to create excel file with python.

In the last step you need to write the new excel file created in the field Binary, for this you should used "StringIO" and "Base64".

After you have create you excel file. You can save and link to field binary like this:

def save_excel(self, excel):
     stream = StringIO()
     excel.save(stream)
     encoding_stream = base64.encodestring(stream.getvalue()
     self.write('your_excel':encoding_stream)

And with this you can showing your wizard.