The product page for that buzzer says "current consumption: 20 mA" These piezo buzzers can be corrected directly to a DC supply. There is no need for a current-limiting R (as for an LED).

We’d seen it done with buttons, switches, gestures, capacitive touch, and IR remote, but never like this. [electron_plumber] made an LED that can be blown out like a candle, and amazingly it … ...

If our example resistor ended in gold (orange, white, black, gold), its 39 Ohms value could be five percent higher or lower. For a possible minimum of 37.05 or a maximum of 40.95.