You can snooze an alarm by telling Alexa: "Alexa, snooze" while the alarm is sounding. The alarm will go off again 9 minutes later. Currently, Alexa has not enabled the snooze time to change.
You also set up multiple alarms spaced out a few minutes after one another if you want a more precise snooze.
You can also tell Alexa: "Alexa, set a timer for 3 minutes" or some other time. These are unofficial ways that other Alexa users have recommended to replicate a typical snooze function.