What does Stevens do for Goodwin letting her know "everything is going to be ok" in "Source Code"?

In Source Code, Stevens sends Goodwin a message telling her that everything is going to be okay. The message is an email sent from the alternate reality he reaches at the end of the film, proving that his actions have created a new timeline rather than merely replaying the past.

Captain Colter Stevens has been sent repeatedly into the final eight minutes before a train bombing. His military handlers initially believe the Source Code program allows him to reconstruct a past event, but Stevens discovers that each completed mission can produce a distinct reality.

After stopping the bombing and identifying the terrorist, Stevens uses the train’s computer to send Goodwin an email. The message describes what happened and asks her to help the version of him still trapped in the Source Code facility. The film’s final scenes use that message to confirm the hopeful twist.