I'll tell him/her
Bien sûr que je vais lui dire.
Of course I'll tell him.
I'm going to say goodbye to him.
Je vais lui dire que tu as dit ça.
I'll tell him you said that.
Bien, je vais lui dire, que vous êtes occupée.
Okay, I'll tell him that you're busy.
— Romance de bureau (1977)
I’m going to say yes to him/her.
Tu crois que je vais lui dire ?
Do you think I'm going to tell him?
I'll have a word with him.
I'm going to say hello to him.
Je vais lui dire que vous êtes d'accord.
I'll tell him you agree.