Alarm rings before set alarm time

Smart alarm is enabled (see Smart wake up), so the app is waking you within the smart period, when light sleep is estimated.

If this is not what you expect, disable smart period altogether, or try a shorter smart period.

Go to Settings → Alarms → Smart wakeup → Smart period for all your alarms, or for one alarm in alarm → Smart period.

The shortest period is 5 minutes, the longest is 2 hours.