Frodo could be one. Since he was also closely associated with the ring in the original story, he might play a role in this fanfic, perhaps as a supporter or someone who has doubts about Bilbo's ability to destroy the ring.
Bilbo might adapt by using his wits. He's always been a clever hobbit. In an earlier time period, he could use his knowledge of future events to his advantage. For example, if he travels to a time before the discovery of certain paths in Middle - earth, he could be the one to find them first, which would help him in his quest to destroy the Ring.
Well, one possible plot point could be Bilbo's internal struggle. He might have moments of hesitation, thinking about the power the ring has given him in the past. Another could be the reaction of his friends and the surrounding world when he decides to destroy it. Maybe some would try to stop him, fearing the consequences.
Well, in many fanfics, Bilbo might use the ring's power of invisibility. He could simply slip the ring on his finger and blend into the shadows of Erebor's vast halls. Maybe he uses it to avoid detection by the dwarves when he wants to be alone or to secretly observe things going on in Erebor without being noticed.
In some fanfics, using the ring in Erebor could have a negative impact on Bilbo himself. The ring has its own sort of corrupting influence. So, he might start to feel a stronger pull towards the ring, becoming more secretive and withdrawn from the dwarves. This could potentially damage his relationships with them over time.
Perhaps when Bilbo travels back in time, he finds that the Ring has an unexpected origin or connection to other powerful artifacts. This could lead to a whole new set of challenges and adventures as he has to deal with these new revelations while still trying to destroy the Ring. For example, he might find that the Ring is part of a set of items that need to be dealt with together in a specific order.
You can use 'ring ring ring ring' as a signal for something exciting in the story. For example, in a story about a wizard's apprentice, the 'ring ring ring ring' could be the sound of a magical alarm that warns of a dragon approaching.
One bedtime story could be about a magical bell that goes 'ring ring ring ring'. The bell is in an enchanted forest and every time it rings, it wakes up the little fairies who then start their day of spreading magic and kindness in the forest.
One way to develop Bilbo in this fanfiction is by exploring her femininity. She could bring a different set of skills or qualities. Maybe she has a better intuition or is more in tune with nature. As she goes on the adventure, she could use these qualities to her advantage, and this would not only help in the story's progression but also in her own development as a character. For example, her intuition could lead her to find hidden paths or sense danger in a different way than a male Bilbo would.
Maybe Gandalf could help. He's wise and might have some knowledge about hair - cutting. Or perhaps one of the dwarves, like Thorin, who could offer some practical advice or even do the cutting for Bilbo.