MacOS: Keychain Access

User must be signed in on the Mac and run the keychain repair / reset while they are logged in.

Option 1 - Update password 

If your old password works in keychain, use that password to update your existing login keychain:

1. Open the Keychain Access app, which is in the the Utilities folder of your Applications folder.
    
2. From the list of keychains on the left side of the window, select login.
    
3. From the Edit menu in the menu bar, choose Change Password for Keychain login.
    
4. Enter the old password of your user account in the Current Password field. This is the password you were using before the password was reset.
    
5. Enter the new password of your user account in the New Password field. This is the password you're now using to log in to your Mac. Enter the same password in the Verify field.
   
6. Click OK when done, then quit Keychain Access.

Option 2 - Reset Keychain
(if repair fails to resolve issues)

Source: Apple Support

1. Open Keychain Access, which is in the Utilities folder within the Applications folder.
   
2. From the Keychain Access menu, choose Preferences.
   
3. Click General, then click Reset My Default Keychain.
   
4. Authenticate with your account login password.
    
5. Quit Keychain Access.
    
6. Restart the computer.