Question: how to change forgotten keychain password?
Answer: Click on Finder > Go > Utilities > Keychain Access. ... 
From the Keychain Access menu, select Preferences. ... 
Click Reset My Default Keychain. ... 
In the Password field, enter your Active Directory (AD) password (what you log into the computer with). ... 
If desired, click the checkbox to enable Show Password.
Click OK. ... 
Click OK.