Perhaps they could have used time travel to team up with alternate versions of themselves. So, the Avengers from different timelines could combine their powers and knowledge to come up with a better plan to stop Thanos. This would involve not just fighting him physically but also outsmarting him in terms of his knowledge of the Infinity Stones.
Maybe they could use the Quantum Realm not just for time travel but also to create some sort of energy wave that counteracts the effects of the Snap. The characters in the fanfiction could figure out a way to harness the unique properties of the Quantum Realm, which is already a bit of a mystery in the MCU, to fix what Thanos did.
One way to 'fix' the situation in a fanfiction could be to have Loki's faked death in Thor: The Dark World be more thoroughly investigated by Thor. If Thor had been more suspicious and dug deeper, he might have uncovered Loki's real plan earlier. This could have led to them working together more effectively against Thanos in Infinity War, preventing some of the tragedies that occurred.
In this kind of fanfiction, Peter Parker might use time travel to prevent the events of Infinity War. Maybe he could go back in time to warn the Avengers about Thanos' plan earlier. This could lead to a completely different outcome, like they could gather more powerful forces or find a way to stop Thanos from getting all the Infinity Stones in the first place.
Doctor Strange is often a popular character. Given his knowledge of the mystic arts and his ability to see different futures in the movie, it makes sense that he would play a key role in time travel fanfiction. He could use his powers to manipulate time more precisely.
One interesting concept could be alternate timelines. For example, characters might travel back in time to prevent Thanos from getting all the Infinity Stones in the first place. This could lead to a completely different outcome in the war.
In a fix - it fanfiction, Thor and Loki could start by having an honest conversation. Loki could reveal his true intentions and fears to Thor. This newfound honesty could strengthen their bond and make them a more effective team against Thanos. Instead of the constant mistrust between them, they would be united and support each other throughout Infinity War.
One interesting plot could be that the Avengers travel back in time to stop Thanos from ever being born. This would be a radical approach but could potentially solve the problem once and for all. They would have to deal with the moral implications of changing the timeline in such a major way.
A major theme is the power of knowledge. Since the time traveler has knowledge of future events, they use it to their advantage to fix things. Also, the theme of fate versus free will is often explored. Some stories show that despite the time traveler's efforts to change things, fate still has a way of working things out in a similar way, while others show that free will can completely rewrite the future. In addition, the idea of self - discovery is common as characters often learn more about themselves when they go back and face their past.