How can I cancel play a sound on find my iPhone application?

You do not have to cancel it. Here I show it works-

• If the device is online, a sound starts after a short delay and gradually increases in volume, then plays for about 2 minutes. A Find My [device] alert also appears on the device’s screen.
• If the device is offline, the sound plays the next time it connects to a Wi-Fi or cellular network.

More information here-->>Play a sound with Find My iPhone on iCloud.com - Apple Support

Hope that helps.

Axel F.

Good question. I am not sure of the answer to this specific question. What happens if the iPhone is unlocked first then will the sound still play? Good questions.

Axel F.