Environment setup for working with webpack and react

I inherited a number of websites at our company that were development using webpack as well as react. I have been struggling for a week trying to make a small change to site but I can’t get the setup of webpack correct in order to build the site.

My branch

This is the latest output:
Error: Cannot find module ‘webpack-cli’
Require stack:

  • C:\Users\mjackson.ZENEX\AppData\Roaming\npm\node_modules\webpack\bin\webpack.js
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:880:15)
    at Function.Module._load (internal/modules/cjs/loader.js:725:27)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at C:\Users\mjackson.ZENEX\AppData\Roaming\npm\node_modules\webpack\bin\webpack.js:142:5
    at processTicksAndRejections (internal/process/task_queues.js:93:5) {
    code: ‘MODULE_NOT_FOUND’,
    requireStack: [
    PS C:\Users\mjackson.ZENEX\Documents\GitHub\Zenex>

Is there anyone that is very familiar with webpack and the setup and willing to help?