Of course, you'll need to know the old password as well to make this tweak. The solution here is to update the keychain password to match the new password of your user account. Now let's get back to the original problem. You'll have to import them from the old keychain. Even if the keychain password now matches your account password, your password entries are gone. This automatic keychain creation is only partially helpful.
Your old one sticks around you'll find it under ~/Library/Keychains, with the word renamed in its name. When you change the user account password on High Sierra, macOS creates a new keychain for you. As a result, macOS prompts you to enter that when any function requires access to the keychain. The reason for this is that the login keychain still works with your old password.
It occurs when you have changed the password for your macOS user account. You might encounter this problem on macOS versions older than High Sierra.
