The Beretta 92S like the newer 92FS has a front sight that is integral to the slide. Furthermore, because of the open slide design, the part of the slide that the integral sight attaches to is the relatively short, closed front end that holds the whole slide together. I have read that there is not enough metal there to safely mill a dovetail without critically weakening the slide. Before asking a gunsmith to do this, I would make some inquiries.
It is possible to drill the front sight of an FS for a tritium insert, or perhaps you could try one of the Hi-Viz type light absorbing inserts. If this is not sufficient I think you would have to ask a smith about building up the front sight somehow, but I suspect this would also require replacement of the rear sight if the front sight height was increased or dramatically thickened.
This is from another forum. They also talked about Wilson's Combat doing some work but you have to have the FS oversize hammer pin.

You can go aftermarket as 92 sights abound aplenty from Meprolight - TruGlo etc. Beretta also have much improved sights if you wish to remain OEM here : berettausa.com/en-us/store/gun-accessories/accessories-for-handguns/rear-and-front-sights/

fixed front white dot and rear adjustable