Resolve lack of access in Keychain Access
You can log it out without the password. First press command+space and search activity monitor and press enter, then in the search bar in the corner search "loginwindow" without quotations and double click on the one that has the other users name by it. After that you should see a quit option. click it and it will give you 3 choices. Cancel, force quit, and quit. i recommend only force quitting if it isn't responding or if it doesn't work with regular quit. Also, this deletes any unsaved files and/or open tabs you have without saving them, so you might lose some data. About the Keychain password, i have the same question.