If you know your old password, use that password to update your existing login keychain:
Open the Keychain Access app, which is in the the Utilities folder of your Applications folder.
From the list of keychains on the left side of the window, select "login."
From the Edit menu in the menu bar, choose “Change Password for Keychain 'login.'”
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.
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.
