oh i thought you were trying to kerf the port, to round it over, take a router with a .25" round over bit, and just hit all the edges you want to round over.
You'll need to be more specific about the box that it is in to determine what edges would actually need to be rounded. I'm assuming that the picture is of the actual port but how it fits isn't explained at all.
What he is doing is for a 4th order BP enclosure. On the side the sits in the enclosure you need to round over the inside edge and outside edge. On the outside you only have to round over the inside, but it does not hurt to do both inside/outside of the port in your situation.