Samsung
Change Timer Sound auf Samsung
The Timer sound on Samsung phones is controlled separately from your ringtone and notification sound. It sits inside the Clock app itself, not in the general system sound settings, which is why many users cannot find it at first.
This setting only affects the tone that plays when a timer you started reaches zero. It does not change alarm tones or notification sounds for other apps.
Menu path to change the Timer sound
Open the setting with this path:
Tap on Clock ➔ Open the Menu ➔ Tap on Settings ➔ Tap on Sound ➔ Set a Timer sound
From the sound list you can pick one of the built-in tones or select a custom audio file stored on the device. The change applies to every timer you start afterward, until you pick a different tone again.
If the timer stays silent even after changing the tone, check that media volume is turned up and that Do Not Disturb is not muting app sounds. That is a separate volume issue, not a wrong tone selection.