Can’t find fall detection

Hello and welcome to Apple Support Communities, kota48!

I understand you're not seeing the option to enable fall detection in the Watch app. I'd be happy to provide information to help you address this.

Make sure you've entered your date of birth in your Medical ID: Use fall detection with Apple Watch

"Set up your Medical ID and add emergency contacts

1. Open Settings on your iPhone, then tap Health > Medical ID.
2. Tap Edit. 
3. Enter your date of birth and other health information.
4. To add an emergency contact, tap the add button  under emergency contacts. Tap a contact, then add their relationship. 
5. To remove an emergency contact, tap the remove button  next to the contact, then tap Delete.
6. To make your Medical ID available from the Lock screen, turn on Show When Locked. In an emergency, this gives information to people who want to help.
7. Tap Done.

You can't set emergency services as an emergency contact."

Once this is set, you should be able to turn off fall detection.

Regards.