1. A literary agent can represent the project and take it to Lifetime
2. You can write a treatment and along with the book, pitch it to Lifetime
3. You can actually write the script and have it read by Lifetime
Sounds easy enough right? Except, that Lifetime won't read unsolicited material and unless you have an agent, or an entertainment attorney, there's "grass-roots" work that needs to be done.
My first question to you is: Is Lifetime the only network this book/movie is right for? If so, you're going to have to create relationships with people in development there, because they are literally the only people who would make your movie. Therefore, you may or may not want to spend the time going after an agent to rep the project.
It's difficult to answer this question more specifically, because I don't know your relationship to the industry (this question comes from Twitter). If you have no connections at all, I'd give you a very different answer than if I knew your self-published book had sold a million copies and you have interest from agents.
And then finally, there's a query letter that you can send. You can google how to write that, and research the right person to send it to at Lifetime. If they have an interest in the book and the synopsis of your story to be made into a screenplay, they'll ask for more.