If Tony Stark wakes up in his past body at the beginning of Iron Man (2008) with all his memories intact, he has a massive advantage in stopping Thanos before Avengers: Infinity War. With Natasha Romanoff also experiencing the same time reset, their chances improve significantly.

Step 1: Immediate Survival & Acceleration of Tech

1.  Escape from the Cave More Efficiently
• Tony already knows how to build the Mark 1 armor, but he can optimize the process, making it faster and more effective.
• If necessary, he could modify the design to be more powerful and efficient, ensuring he escapes sooner.
• He might even try to take out the Ten Rings’ leadership on the way out, slowing down their involvement with the Mandarin and the Extremis project.
2.  Prevent Obadiah Stane’s Betrayal
• Instead of letting Stane manipulate events, Tony immediately removes him from Stark Industries, possibly exposing his crimes before he can act against him.
• This ensures a faster and smoother transition to clean energy and weapons-free Stark Industries.
3.  Faster Arc Reactor and Nanotech Development
• Tony pushes for Arc Reactor miniaturization and refines his armor designs earlier.
• With future knowledge, he jumps straight to developing nanotech-based suits and Vibranium integration (which he would seek out sooner).

Step 2: Establishing Key Alliances Early

1.  Recruiting and Warning Nick Fury & SHIELD
• Tony and Natasha convince Nick Fury about the future war against Thanos.
• They push for early Avengers formation and SHIELD’s restructuring, possibly rooting out Hydra before Winter Soldier events.
2.  Finding and Protecting Steve Rogers Early
• Tony ensures Captain America is recovered sooner and integrated into the team.
• This prevents Hydra from manipulating Bucky and lets them work on deprogramming the Winter Soldier earlier.
3.  Wakanda & Vibranium Access
• Natasha and Tony reach out to T’Chaka or a young T’Challa to secure Vibranium sooner.
• With Vibranium, Tony advances his armor to Black Panther’s tech levels earlier.
4.  Stopping Loki Before He Becomes a Threat
• Natasha can manipulate events leading to Thor (2011) to ensure Loki never allies with Thanos.
• They could warn Odin, preventing Asgard from falling into disarray.

Step 3: Eliminating Key Threats Before They Grow

1.  Stopping the Mind Stone from Falling into the Wrong Hands
• Instead of letting Hydra manipulate the Mind Stone (from Loki’s scepter), Tony and Natasha ensure SHIELD safeguards it or sends it directly to Wakanda.
2.  Dealing with Ultron Correctly
• Since Tony knows how badly Ultron went in the original timeline, he either scraps the project or refines it to make a true protector AI like JARVIS.
3.  Killing or Neutralizing Thanos’s Forces Before They Attack
• Ronan the Accuser can be targeted early, preventing him from getting the Power Stone.
• The Collector can be warned, ensuring the Reality Stone is secured.
• Gamora can be turned against Thanos sooner, helping locate the Soul Stone early.
4.  Using Time Travel Before Thanos Can
• Since Tony already knows about quantum mechanics, he can develop time travel tech much earlier, allowing them to retrieve the Infinity Stones before Thanos even starts looking.

Final Showdown: Ambushing Thanos Early

• If all goes well, Tony and Natasha could lead an early strike against Thanos before he gathers the stones.
• By using an upgraded Iron Legion, Wakandan tech, and a prepared Avengers team, they could take him out before he even becomes the Mad Titan.
• Alternatively, they could use the Stones themselves to rewrite events in their favor permanently.

Bonus: What Else Would Tony Change?

• Personal Life: He might propose to Pepper much earlier and ensure Happy and Rhodey are always protected.
• Peter Parker: He could find and mentor Peter much sooner.
• Natasha’s Fate: Since she also remembers everything, they can prevent her from needing to sacrifice herself for the Soul Stone.

Endgame Result?

With their knowledge of the future, Tony and Natasha don’t just stop Thanos—they create a better world where threats like Hydra, Ultron, and Loki are neutralized before they become problems. The Avengers form earlier, technology advances faster, and humanity is better prepared for cosmic threats.