How do I help another lane (as adc) when they are getting stomped?

Had a game just now that our Ahri was unfortunately getting rofl'd by a Talon. I had no idea how to help. Do I sacrifice a wave or two to gank? What are some other tips especially if they're 3 or 4 deaths down by 6? Is that just ganking a losing lane as a jungler? Just hope you can team fight it out and your team can keep Talon off of you (despite him kind of designed to get around a bunch of that)