I also feed Repashy CGD, but I breed fruit flies deliberately to feed to my little lizards, so... <lol>

But the wild, flighted fruit flies, it's really quite simple. Close the windows, and change the food out every other day. The fruit flies will not have enough time to reproduce, and should go away fairly quickly.
Be sure you dispose of the old crested gecko food down the drain, and not just toss it into a garbage can where the flies will gladly complete their life cycle.

If that doesn't work, then your real problem is, WHERE ARE THEY COMING FROM. They're obviously not coming from the CGD, so where are the flies breeding in your home? Or do you need tighter window screens? Because if you have fruit flies breeding elsewhere (such as in your kitchen) you need to deal with them there. You can't blame the CGD for attracting flies without realizing the flies have to be attracted FROM somewhere.

Don't feed your geckos nothing but dusted crickets just because you don't like fruit flies. Crested geckos need CGD, not just crickets. If you cannot handle the problem some other way, you should re-home the animal. Don't compromise his well-being for the sake of a few harmless nuisance flies.

The CGD is not to blame. If you didn't have that, then the flies would be after your tomatoes, or any fresh fruit you left out, or banana peels in the garbage, whatever.