Is there a way to label alarms on the viviactive 3? Like if I want to put a mantra on my watch, how can I set up reminders?

You can use Google Calendar or Office 365 Calendar (whatever you have linked to your GC account), and schedule the notifications there. It allows you adding the title, text, time, and the periodicity too. The notification will then pop up on your watch, when scheduled. If you need a stronger or longer alarm than the one used for notifications, you can combine it with a true alarm.