Originally, the keychain password is the same as the login password for the account. The login password can be changed in any of three ways:
- By the user, in the Users & Groups preference pane. In this case, the keychain password is automatically changed to the new login password
- By the administrator (if different), also in the preference pane. The keychain password is not changed.
- By anyone who has physical access to the computer, in Recovery mode. The keychain is replaced by a new, empty one with the new password, and the old keychain is saved with the old password.
To change a keychain password, launch the Keychain Access application and select the keychain from the list on the left. If the list isn't showing, select
View ▹ Show Keychains
from the menu bar, or press the key combination command-K. Then select
Edit ▹ Change Password for Keychain...
You must know the old password in order to set a new one. Otherwise you'll have to reset the keychain.
Apple would not charge you to solve this problem. You must have searched for something like "Apple Support" and then called one of the fake tech-support scams that infest the search engines.
The warranty entitles you to complimentary phone support for the first 90 days of ownership.