Unable to implement migration command

I’m not a developer. I’m just a lay user trying to get a JSON file from my Substack zip export so that I can import it into Ghost Pro Labs page and import my posts (not my subscribers, but posts).

I have seen the Official Substack to Ghost migration guide/document and tried to follow the instructions.

I install the Ghost-CLI and have used

npm install --global @tryghost/migrate

But when I type ‘migrate’ (sans the quotes) in the cmd to test the installation, I get the error

Error: ENOENT: no such file or directory, open '\C:\Users\xxxx\AppData\Roaming\npm\node_modules\@tryghost\migrate\package.json'
    at Object.openSync (node:fs:585:3)
    at Object.readFileSync (node:fs:453:35)
    at file:///C:/Users/xxxx/AppData/Roaming/npm/node_modules/@tryghost/migrate/bin/cli.js:8:35
    at ModuleJob.run (node:internal/modules/esm/module_job:185:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:281:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:65:12) {
  errno: -4058,
  syscall: 'open',
  code: 'ENOENT',
  path: '\\C:\\Users\\xxxx\\AppData\\Roaming\\npm\\node_modules\\@tryghost\\migrate\\package.json'

Please, any help would be appreciated; I will do my best to help you to help me. I just want to import my posts to Ghost Pro via a JSON file.