Embeddable app login to sandbox

Hello,

I have cloned the Ring Central Embeddable Electron App repo, as a starting point. The repo configures a <webview> to render the RC login screen, as follows:

<webview
  preload="./preload.js"
  partition="persist:rcstorage"
  allowpopups
  id="rc-widget-adapter-frame"
  src="https://ringcentral.github.io/ringcentral-embeddable/app.html">
</webview>

How can the source be configured to log into the sandbox environment instead of production. i.e. https://login.devtest.ringcentral.com/