my apple watch locked up because I forgot my password. how do i solve this problem

Follow these steps:

1. Put your watch on its charger and keep it there until you complete these steps.
2. Press and hold the side button until you see Power Off.
3. Press and hold the Digital Crown until you see Erase all content and settings.
4. Tap Reset, then tap Reset again to confirm.
5. Wait for the process to finish, then set up your Apple Watch again. When asked, restore from a backup.

For more info, go here: https://support.apple.com/en-us/HT204567