The Fitbit Community is a gathering place for real people who wish to exchange ideas, solutions, tips, techniques, and insight about the Fitbit products and services they love. By joining our Community, you agree to uphold these guidelines, so please take a moment to look them over.
I don't use the alarms myself but here's a link. You have to tap on On Device for all of the sections as there isn't a way to do it in the App for the Charge 5.