Okay it lands in a melted state and Rey finds it on her scavenging travels,not realising what it is, repairs it and makes it more powerful and then becomes intrigued with the force and the backstories and realises she has a natural ability with the saber, yet to realise that she is indeed force sensitive.
Or she just finds it one day partially buried in the dirt. We don’t know whose it was. Some Jedi, maybe, who died in the Clone Wars, or something. Its origin is unknown. She finds it one day, and it changes her life.