Never tell “don’t be afraid”. Trying to prevent emotions messed up the mind, as it puts the voluntary mind against the involuntary. It often fails and makes things worse.
Instead say, “if you’re afraid it’s ok, …”. You want to induce any fearful member of the audience in a state of awareness, non-shame, and curiosity about how they’re going to learn _despite_ the fear: in short, you want to instill courage.