Lubrication will not always do the trick if the stiff link is seized in there tight with rust and not moving at all. If you have a chain tool, you can pop the pin most of the way out and flex around the link to get it moving again then pop the pin back in and flex the link again to loosen it. Otherwise you can try to set the chain into some sort of vice and use leverage to get that link moving. Or just live with a chain that skips every few revolutions.