How can I do a hard reset on my Apple Watch?

If you mean a forced reset to clear software glitches (like rebooting a computer) just press and hold both buttons about 10 seconds until the Apple logo appears, then release and let the watch reboot. If you mean you want to do a full factory reset you need to unpair or erase the watch (same thing, different words) see If you forgot your Apple Watch passcode - Apple Support which was written for a different purpose but the procedure works.

Hi alecia290,

Try following the steps in this article: How to restart your Apple Watch - Apple Support

Hope this helps.