You can make a gun shoot higher by filing its front sight down. Be careful. Do it a little at a time. File a little, shoot it to see the effect, and then maybe file some more.
If your boyfriend has been shooting guns all his life, and he is an instructor, I am surprised that he did not already know this.
Just to be absolutely safe about this matter, I am compelled to add that new pistol shooters almost always find their pistols shooting low. It is a problem of the shooter's technique, not of the gun.
Hold onto the pistol as tightly as you can with your thumb and three lower fingers, while leaving your index finger relaxed enough that it can press the gun's trigger gently straight back. Let the shot go off as a complete surprise. If you maintain a good sight picture, you will hit the target correctly, and you will see that the problem is not the gun's fault.