Change a weak password on iPhone
If you create your own passwords and any are weak (for example, they’re easily guessed or used multiple times), iPhone identifies them for you automatically.
Go to Settings
> Passwords > Security Recommendations.
If an account has a weak password, a message explains the problem.
Tap the account.
Tap Change Password, then change your password on the website or in the app.
If the website or app allows you to upgrade to Sign in with Apple, you can take advantage of the security and convenience of that feature. If you aren’t given the upgrade option when you change your password, for many accounts you can let iPhone automatically create a strong password that you don’t have to remember.
Note: The Delete Password button allows you to remove the password from your iCloud Keychain only. It doesn’t remove the weak password from your website or app account.
iPhone also securely monitors your passwords and alerts you if they appear in known data leaks. If you don’t want iPhone to perform this monitoring, go to Settings > Passwords > Security Recommendations, then turn off Detect Compromised Passwords.
If iPhone warns you of a weak password for a website or app that is no longer available, you can remove the account from your iCloud Keychain. To remove an account, go to Settings > Passwords, then swipe left on the account.