When one doesn’t know what to say, the best advice is often to keep silent.
Here is an expression of the typical theme of the virtue of restraint in speaking. “Some people keep silent because they have nothing to say, while others keep silent because they know when to speak” (Sirach 20:6; see also the context. See also Proverbs 13:3; 17:28; 18:2; 29:20; Ecclesiastes 3:7b). Jewish tradition asks, “How is one to distinguish the silent sage from the silent fool?” The answer, “The sage doesn’t mind being silent.”