Here are various ways to get rid of an alarm:
Swipe left over the alarm to turn it off.
Go to Edit, then to the Erase button, then to Delete something.
Select Edit, then the alarm, and finally Delete Alarm from the drop-down menu.

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If the volume is too low or mute, Do Not Disturb and the Ring/Silent switch have no influence on the alarm sound. Even if your Ring/Silent switch is set to Silent or Do Not Disturb is turned on, the alarm continues to ring.
If your alarm doesn’t go off or is too quiet, or if your iPhone simply vibrates, check the following: Adjust the volume on your iPhone.

Change the volume of your alarm if it is too low or too loud by tapping the volume up or down buttons. In Settings > Sounds & Haptics, you may also drag the slider under Ringer and Alerts.
If your alarm only vibrates, make sure the sound isn’t set to None. Select the Alarm tab in the Clock app, then select Edit. Go to Sound and select a sound after pushing the alarm.

If you connect headphones to your iPhone, the alarm will play at a preset volume via the built-in speakers that is on your iPhone as well as the wired and wireless headphones and speakers.

Manually adjusting the time on your iPhone in Settings to alter app behavior, such as gaming timings, is not recommended and may cause alarms to malfunction. This is why: Ringer volume regulates the volume of the ringer, notifications and system warnings, and alarms on iOS, whereas media volume controls the volume of games, music, and videos in addition to calls. Because your alarm volume is linked to your ringer volume, altering it before bedtime could mistakenly mute your alarm.
To ensure that your alarm is loud enough to wake you up, follow these steps:

Increase the volume

Go to the home screen to change the ringer volume, not the media volume. Use the volume control buttons on the home screen to alter the ringer volume. Because the volume meter on your screen is labeled “Ringer,” you’ll know you’re setting the ringer volume.

You may have your phone set to alter media volume via the volume buttons if the volume meter on your screen happens to be labeled “Volume” rather than “Ringer.” Go to Settings, then Sounds & Haptics to solve this. A toggle switch titled Change with Buttons may be found under Ringer and Alerts. Turn this toggle on to use the volume buttons on your phone to change the ringer volume.

Use the silent mode on your phone

If you’re sleeping through your alarm, it’s possible that you’ve turned the ringer volume on your phone all the way down before going to bed. Instead of using the volume buttons to silence your phone throughout the day, simply turn off the ringer with the quiet switch (above the volume keys). The ringer on your phone will be turned off, but your alarm will remain active.

Make sure your alarm is set

From the alarm settings screen, you can determine how loud your alarm will be. To do so, launch the Clock app and select Alarm from the menu. Select the alarm you want to check by tapping Edit in the upper left corner. Tap Sound then selects the alarm tone you’d like to use.