Tony ends the first film by telling the world "I am Iron Man."
In the final battle Tony takes the Stones from Thanos, says "I am Iron Man" and snaps his fingers.
Tony's first and last big lines are the same words. The Endgame line was not in the original script; it was added in post-production and shot in reshoots.
Source: Screen Rant: Avengers: Endgame Crowd Shocked By Tony Stark's I Am Iron Man Scene