Here's one of many ways. Probably need a fair amount of tweaking to suit your exact needs.
Option Explicit
Sub FillRng()
Dim i As String
Dim c As Range
i = "A Choice"
' i could be an item from a drop down list
' If so then i = range("A1").value (drop down in A1)
For Each c In Range("E2:G10")
If c.Value = "" Then c.Value = i
Next