Using vba -how do I remove characters from right of space on all cells in specific columns

Sorry if this is a stupid question, but I am new to vba and I am trying to remove characters from the right of a space

an example of the text in the cell is - 5/08/2015 at 12:22 PM

I want to reduce it to 5/08/2015 (formatted as d/mm/yyyy)

Dim tmp As String
Dim DateOnly As String
tmp = Range("E3").Value
DateOnly = Left(tmp, InStr(tmp, " ") - 1)
Range("E3").Value = CDate(DateOnly)

this removes the time from the end of the one cell, but I am struggling to get it to work on all cells within 3 columns ("E:G")

Can anyone assist please?