to address someone formally, use vous with someone
And there's no need to address me formally.
— Une femme fantastique (2017)
Déjà, pas la peine de me vouvoyer.
For starters, there's no need to address me formally.
— Une femme fantastique (2017)
Mais tu ne vas pas me vouvoyer.
But you're not going to address me formally.
— Femmes au bord de la crise de nerfs (1988)