Dumbledore could also play a role. He is the headmaster of Hogwarts and has a vast influence. He might arrange for Harry to have a job at Hogwarts, perhaps something related to the library or the school's security during the summer months. He always has plans for Harry and getting him a job could be part of one of his schemes to further Harry's growth and understanding of the wizarding world.
Hagrid could be a great help. He has a lot of connections in the wizarding world, especially with those related to magical creatures. He might introduce Harry to someone who needs help with taking care of or studying magical beasts, and thus get Harry a job in that area.
He could work at Weasleys' Wizard Wheezes. He has a good relationship with the Weasley family, and it would be a fun place for him to work, helping with inventing and selling all kinds of magical pranks and toys.
He could meet other young wizards and witches who are also working summer jobs. Maybe some from other wizarding schools.
He could work at Flourish and Blotts. He's very knowledgeable about magic, so he could help customers find the right books. It would be a great job for him as he loves to read and study magic. He could also recommend books to young witches and wizards starting their magical education.
Perhaps Harry gets a job as a magical tutor for some young wizards. The story could develop as he tries to teach them the things he's learned over the years. He'd face challenges like dealing with difficult students or trying to teach advanced magic to those who are not ready. His experiences at Hogwarts would come in handy, but he'd also have to learn new teaching methods.
Well, he might work at Weasleys' Wizard Wheezes. He could help George and Ron with inventing new products and dealing with customers. It would be full of magical mishaps and lots of fun.
Obviously Harry would be one of the main characters. And Hermione might also be involved, perhaps she helps Harry get the job or gives him advice on how to do it well.
Well, he could work at Hogwarts during the summer for a change. Maybe he's helping Hagrid with the care of magical creatures. He would get to interact with new and dangerous beasts, and at the same time, he might learn some new spells to keep them in check from other professors.
Maybe Dumbledore, if he were still alive in the fanfiction. Dumbledore was highly respected and had a great influence. Knighting Harry would be a way for him to publicly recognize Harry's achievements and heroism on a grand scale.
His friends from Hogwarts, like Ron and Hermione, are likely to help. Ron could bring his family's practical knowledge of wizarding homes and Hermione would contribute with her extensive research skills.
Hermione would be a great help. Her vast knowledge of magic and books could provide the necessary information for building the planet, like the right spells and magical theories.