Naruto has been through a lot in his own time, so he may use that experience to adapt to the past. He might start by making friends with the younger versions of people he knows. He'll also have to be careful not to reveal too much about the future to avoid disrupting the timeline. He could use his ninja skills to earn respect and find his place in the past world.
I would recommend 'Naruto's Childhood Redefined'. This fanfiction focuses on Naruto's early years in a different way. It adds some interesting backstories to his relationships with Iruka and the villagers. It's a great read if you want to see a new take on Naruto's past.
He might try to change certain events. For example, he could prevent some of the tragedies that occurred in the original story. Maybe he would stop the Uchiha massacre by warning the clan or finding a way to resolve the conflict between the Uchiha and the village leadership.
He would probably use his leadership skills. Naruto has grown into a great leader as Hokage. In the past, he could quickly assess situations and lead others, whether it's in a battle or in village - building activities.
Well, in a fanfiction where Naruto travels to the past, he could meet his parents when they were young. He could also learn new jutsu from the past ninjas that were lost over time. Maybe he'd even be able to influence the early development of the Hidden Leaf Village in ways that would make it stronger in his own time.
There are quite a few things. For one, he could teach past Naruto about the deeper secrets of the Uzumaki clan. Since Future Naruto has explored more about his heritage. He could also give tips on handling the Kyuubi's chakra more smoothly. Maybe some new jutsu combinations that he discovered over the years. And not to forget, how to better read an opponent's moves during a fight, which is a skill he would have refined over time.
Naruto could also meet the previous Hokages in their prime. He could learn from them directly and perhaps even influence their decisions. For example, he might be able to convince the First Hokage to handle the Uchiha clan's situation differently, which could have a huge impact on the future (or in this case, the future that Naruto comes from).
Naruto would meet his younger self. This would be a really strange situation. He could also meet all the important shinobi from the past. For example, the First and Second Hokage. He might have a chance to learn from them directly, instead of just hearing about them in stories. Additionally, he could meet some of the characters who were only mentioned in passing in the original story but had a big influence in the past.
One great 'Return to the Past Naruto Fanfiction' is 'Naruto: Back to the Beginning'. It has an interesting plot where Naruto goes back in time and uses his future knowledge to change things. He's able to prevent some of the tragedies that happened in the original story.
He would probably be quite amused by some of his past antics. For example, his constant pranks on Iruka-sensei. But at the same time, he'd also see the pain he carried from not having his parents and realize how that influenced his actions. He might react with a bit of regret for some of the stupid things he did out of loneliness, but also be glad that those experiences made him who he is today.