Question: I am currently writing a book whose protagonist is loosely based on my own experiences. How do I move from autobiography to fiction?Answer:
So you want to take your own experience and base a fictional work on it?
I suggest you start with a brief summary of the story - use the 8 elements of plot to create your summary. (See https://www.how-to-write-a-book-now.com/plot-development.html)
Then ask yourself what one thing you could change to turn it into the kind of story you would enjoy writing.
For instance, you could change...
* the setting (time as well as place)
* the genre (romance, mystery, literary, fantasy, etc.)
* the main character (sex, age, occupation, etc.)
* any other key detail
Create new plot summary with the change. Make a list of questions a stranger could ask about it. Brainstorm possible answers to these questions, and incorporate the answers you like.
Even if you only get part-way through this process, you should have a very different story to work with, that still retains something of the original.
From then on, develop the story just as you would any other work of fiction.