Hi Plumbster,
You'd want to revoke and create a new password. Here is how.
"How to revoke an app-specific password
You can have up to 25 active app-specific passwords. If you need to, you can revoke passwords individually or all at once.
- Sign in to appleid.apple.com.
- In the Sign-In and Security section, select App-Specific Passwords.
- Select the Remove button
next to a password you want to delete, or Revoke All.
After you revoke a password, the app using that password will be signed out of your account until you generate a new password and sign in again.
Any time you change or reset your primary Apple ID password, all of your app-specific passwords are revoked automatically to protect the security of your account. You need to generate new app-specific passwords for any apps that you want to continue using."
More info can be found here: Sign in to apps with your Apple ID using app-specific passwords - Apple Support
We hope this helps.
Cheers!