How to apply simple macros to only one column

First off, my VBA/Macros is EXTREMELY limited. In fact, I don't really even know what I'm doing when it comes to this stuff.

With that said, I have a simple macros as show below:

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Range, Cancel As Boolean)
Target = "a"
End Sub

which allows me to place a checkmark in the cell on a double click.

I want this to only apply to the N column in my spreadsheet. Is this possible?