My iPhone keeps ringing it’s alarm in silent mode and even in do not disturb mode how can I make my alarm only vibrate?

Edit the alarm. Specifically, the option for "Sound". Scroll all the way to the bottom and select "None".

The alarm rings in silent mode and DND because it is designed to. Many people use it as a wake-up alarm, and they have DND enabled while they sleep. If it didn’t override DND it would be useless as an alarm clock.

If you don’t want it to ring either assign a silent ringtone to it (“none” in the ringtone list), or don’t use the alarm app. Instead use either a calendar event or a Reminder.

That's completely normal.

If you don't want the alarm to play any sound, you can set the alarm sound to none (vibrate only).

• Tap on the Clock app
• Tap on Alarm
• Choose your alarm and turn it on
• Tap on the alarm you just turned on
• Tap Sound
• Scroll to the bottom and tap None
• Tap Back