sveltekit build port is always 3000 but it is not available in my server. How do you change port in svelte.config.js?

Question

Port 3000 is occupied in my hosting server. Now I'm building a sveltekit app. When I use

npm run dev --port 4000

or npm run build and then

npm run preview --port 4000

I'm able to start the sveltekit using localhost:4000

My npm run build is always pointing me to

   [email protected] preview
> svelte-kit preview


  SvelteKit v1.0.0-next.260

  network: not exposed
  local:   http://localhost:3000

after searching online some of the possible solutions available online is to change the port in the adapter-node config env like so:

const config = {
    kit: {
        adapter: adapter({
            out : 'buildit',
             env : {
                port : 4000,
             }

            // vite : {
            //  server : {strictPort : false}
            // }

        }),         
    }
};    
export default config;

I go back and build the sveltekit again then run the command npm run preview again, like so:

npm run build
   npm run preview

but the it gives me the same 3000 port. Some of the discussion online pointed to the vite flag where you set the strictPort to false and it will look for the next available port but that didn't change the port and the build still fixated on port 3000.

When I use npm run build --port 4000, while another app is running on port 3000, I get an error.

Error: listen EADDRINUSE: address already in use 127.0.0.1:3000
    at Server.setupListenHandle [as _listen2] (net.js:1318:16)
    at listenInCluster (net.js:1366:12)
    at GetAddrInfoReqWrap.doListen [as callback] (net.js:1503:7)
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:69:8)
Emitted 'error' event on Server instance at:
    at emitErrorNT (net.js:1345:8)
    at processTicksAndRejections (internal/process/task_queues.js:82:21) {
  code: 'EADDRINUSE',
  errno: -4091,
  syscall: 'listen',
  address: '127.0.0.1',
  port: 3000
}

It seems like it is a server instance error. How to fix it?

It seems like fewer developers are interested in sveltekit because when I used to post a question about sapper, I used to get an answer within hours but I'm noticing that questions about sveltekit getting answered in days. Hopefully there are some developers out there keeping their eyes on sveltekit tag in stackoverflow.

So my question how to change the npm run build so the sveltekit app start using a different port. I'm not asking about npm run dev or npm run preview. My inquiry is about sveltekit to run on port 4000. How the npm run build could be used to build sveltekit app with a different port?