how to define dynamic routes while doing next export command

Basically I want to define dynamic routes like this:

routes->

 /books/categoryname
  /books/categoryname/bookId

categoryname is dynamic and also bookId

folder structure:

books -> 
  index.tsx
  [book_category] ->
    index.tsx
    [id]
      index.tsx

how to define dynamic routes in next.config.js ?

next.config.js

  exportPathMap: async function (
    defaultPathMap,
    { dev, dir, outDir, distDir, buildId }
  ) {
    return {
      '/': { page: '/' },
      '/about': { page: '/about' },
      '/contact': { page: '/contact' },
      '/register': { page: '/register' },
      '/login': { page: '/login' },
      '/books': { page: '/books' },
      '/books/category': { page: '/books/[book_category]' },
      '/books/category/id': { page: '/books/[book_category]/[id]' },
    }
  },
}