Please follow steps below to delete registration data from Apple Watch.
 

1

Go to the screen of digital lock you wish to delete, then proceed to tap "≡" on the top left corner.

  

2

「登録削除」をタップします。

3

Tap "Delete".

Digital lock registration data will remain in the Apple Watch but will be inoperable. 
Due to registration limit, please delete the unused registration data.
For how to delete digital lock registration data from digital lock, please click here.