Where to dig to close gaps in knowledge and close the task?

Question

Node.js

I am creating a project structure (preparing it for further work with it) in ReactJS by copying another project with nextJS. (The question is more in a specific situation, as I understand it from server.js next.js

) enter it so that it works correctly.

What I did:
- I copied the project to the required directory
- I run script dev


- when I build


it, I get it, I need to enter something in the server.js file, but I don’t know what (lines 20 and 27)