If you've forgotten your Keychain password, go to your Keychain Access app, click "Keychain Access," and choose "Preferences" ("⌘"). Click "Reset my default Keychain," and you'll be asked for a password. Please note that it's the one you use to log in to your computer. The Mac will inform you that your old password has been renamed. If you can't reset to your default Keychain because it's grayed out, go to Edit > Keychain list and click "Show." Make sure that "user" is selected; otherwise, click it and use the minus sign ("-") to delete.  When you'll restart and log into your session, the computer will ask you to set up a password for your Keychain, and you can click the "Remember my password" box.