You can export static files simply running the following command (See Next.js document)
npm run build
Remember to check all the exported paths have been properly configured in exportPathMap in next.config.js.
All the static assets will be exported to ./out folder. You can use the following command to run a simple server to see the exported results.
node staticServer.js
npm run build
All of the links to static assets will be added with prefix: appConfig/assetPrefix, which can be configured in config.js