u/Point-Break-__-

I have a plot in, the theme it would circle around, and a climax for it.
What I don't have is the end to end idea of every scene and how to connect and fill the plot, and also no other characters in mind other than the protagonist but that is not an issue cuz it is basically a single character plot (for eg:- Trapped) so that I'll somehow figure out.
BUT how do you start writing on a blank page, anything could be helpful.