How to ask for a new random password to replace one that no longer works from the keychain?

Hello JimRussell and welcome to Apple Support Communities.

I see you are trying to get new password suggestions for web sites on your Mac. The auto-prompt to suggest only comes up when the account is first created. But you can use Keychain Access to get new suggestions.

What is Keychain Access on Mac? - Apple Support

Manage passwords using keychains on Mac - Apple Support

1) Open Keychain Access from the Utilities folder inside the Applications folder

2) In the sidebar on the left, choose iCloud from the Keychains if you're using iCloud Keychain. If that is not available, choose "login" and in the section under that called Category, choose Passwords.

3) Find the entry for the web site for which you're trying to change the password. If the list is long and tough to navigate, you can use the Search box in the upper right. Double click the keychain entry.

4) You'll get an info window about the entry. Near the bottom there is a checkbox called "Show password." Click that.

5) You'll see a request for the keychain password. This will be the same password that you use to log in to the Mac.

6) You'll see the current password and an icon just to the right of that which looks like a key. Click that.

7) You'll see a box called Password Assistant with a new password suggestion. Clicking the downward pointing arrow to the right of the suggestion will reveal other suggestions. Put the cursor at the end of the suggestion and the password will change in the keychain. If you're using iCloud Keychain, the change will migrate out to all devices using that feature signed in to the same Apple ID.

Cheers.

Hi JimRussell.

First, I just realized I left the last two steps in that process out. After you place the cursor at the end of the password suggestion, hit the Return key. That should change the password in the main Keychain Access window. If for some reason it does not, you can just copy the suggestion and paste it into the password box in the main Keychain Access window. After doing that, the button in the lower right called Save Changes becomes clickable. You'll have to click that or the change will be lost when you close the window. You'll also have to use the mechanism on each site to change the password there. Unfortunately, Keychain Access is only about the passwords stored on the Mac or in iCloud. The password associated with your account on each web site would have to be changed individually and at the site itself.

As far as iOS devices go, there is not a current option for password suggestions at Settings > Passwords & Accounts > Website & App Passwords. The best way to handle it is to use process outlined and then use iCloud Keychain to migrate changes across devices. If that is a feature you'd like to see in the future for iOS, leave feedback for Apple here:

Feedback - iPhone - Apple

At the drop-down menu, choose Feature Request.

Cheers.