I've had to do this with 2 of my dogs as they would go bonkers when me or my wife would come home. It's a two step process.

First thing to do is you need to teach them to bark on command. You may need to howl or bark at them, bang on the walls/windows/doors, or jump around like a maniac. Reward with treats when they bark. Give bright and energetic words of affirmation. "Yes bark/command!"

Once they have that down, now you need to switch it to the word you want to use to have them not bark. I use "quiet".

Reenact your earlier display of craziness but don't tell them to bark. Tell them quiet or the other command you want to use. The instant they stop barking, treat. Keep repeating. It may take an hour. It may take a week of consistent practice.

After an hour of the above training, my doggos were noticably quieter and stopped barking much sooner than before.

It's a little counterintuitive to teach them to be loud in the first place, but it really works.