Mail Merge from Excel to word for single row only

I have a customer database for a business which I would like to use for a mail merge.

I have managed to write a macro script which will do a mail merge for every single customer in the database, when a button is clicked on the excel document. I am wanting to set the script so that when the button is clicked, I can choose a single row so that the info on that single row is merged, ignoring all others. I don't mind how this is done, whether it be with a dialog box or by selecting the row and then clicking the merge button (or any other way possible).

Below is the script i currently have for the full mail merge:

PHP Code: 

Sub RunMailMerge()

    Dim wdInputName As String
    wdInputName = ThisWorkbook.Path & "\Referring Practitioner.docx"

    ' open the mail merge layout file
    Dim wdDoc As Object
    Set wdDoc = GetObject(wdInputName, "Word.document")
    wdDoc.Application.Visible = True

    With wdDoc.MailMerge
         .MainDocumentType = wdFormLetters
         .Destination = wdSendToNewDocument
         .SuppressBlankLines = True
         .Execute Pause:=False
    End With

    ' show and save output file
    wdDoc.Application.Visible = True
    wdDoc.Application.ActiveDocument.SaveAs wdOutputName

    ' cleanup
    wdDoc.Close SaveChanges:=False
    Set wdDoc = Nothing

End Sub 


What do I need to add to the script to allow me to single out rows for the merge, so that I don't get hundreds of merged letters every time I click the button?