Usually, drilling through the front sight is not much of an issue, but it can happen.
You did drill through it, so the hole is there. All you have to do now is to find that hole.
Before you can force a pin through it, and damage the pin or the slide, if everything is not perfectly aligned, use a small punch, or a small screw driver to align the slide and the new sight hole together. You might have to play with the new front sight a bit for your punch to find all the holes.
Once this is done, leave the punch in the holes and get your pin started from the other side.
Gently hammer the pin and keep pressure on the punch at the same time for the pin to follow your punch's.
Et voila, everything should fall into place.
Keep us posted with your results.