Hermione might help him. She's always resourceful and would probably come up with a clever plan to get Harry to Hogwarts.
There's also a chance that some new character in the fanfiction, perhaps a friendly wizard who lives near the train station, could help Harry. This wizard could have some unique magic or knowledge that enables Harry to reach Hogwarts despite missing the train. For example, he might know a secret portal or a special spell that can transport Harry quickly to the school.
His friend Ron could come back to help him. Ron is always loyal and might not want to leave Harry behind. He could bring his family's flying car again to pick up Harry.
Maybe Harry has to find an alternative way to get to school. He could use magic to apparate or fly on a broomstick.
Maybe he has to find an alternative way to get to school. He could try to use magic to create a makeshift transportation or ask for help from his friends' families who might be passing by.
The magical creatures could play a role in helping Harry. For example, the centaurs with their deep understanding of the stars and magic could offer their wisdom. The house - elves, like Dobby (if he's alive in the fanfic), might use their unique magic to assist Harry in a time of need.
His friends for sure. Hermione is really smart and could help with things like making sure the baby is healthy with magic, and also helping with any magical problems that might come up because of the baby.
Hermione could be a great help. She is very intelligent and resourceful. She could help Harry find evidence against Snape. For instance, if Snape is suspected of cheating in grading, Hermione could use her knowledge of Hogwarts' grading system and records to dig up proof.
Hermione could be one of the characters to help Harry. She's intelligent and resourceful, so she could provide practical help like finding a good doctor or helping with magic - related pregnancy issues if it's in a magical world. Another could be Hagrid. He has a big heart and could offer emotional support and perhaps a place for Harry to stay if he needs it.
It could be Dumbledore. Even if he's dead in the original story, in fanfiction, anything is possible. He might have left behind some kind of magic that allows him to train Harry from beyond the grave, or he could have faked his death to take Harry to a secret location for training.
Hermione could be a great help. She's very knowledgeable about magic and could research how to properly care for a newly hatched female dragon.
Dumbledore could also play a role. Even if he's not alive in the normal sense, his spirit or some form of his magic could guide Harry. He might have known about the connection between Harry and Excalibur all along and left behind some hints or instructions for Harry to follow.