If Flynn is actually seeking immunity for testimony, he may be wanting discuss crimes committed that helped start this “russian narrative” mess. There is an article in NPR that reports, as other outlets have, that Flynn would not be charged with wrongdoing because he did nothing wrong.
Certainly there are varying opinions on what an immunity deal means. Here’s one opinion, but I’ll admit the source is kinda sketchy.
“When you are given immunity that probably means you’ve committed a crime.”
– Lt. Gen Michael Flynn (Ret), Sept 2016