URL Scheme for switching between 3G and 4G
Do you have an app called Launcher?


  Launcher with Notification Center Widgets by Cromulent Labs
  https://appsto.re/gb/iLR81.i


You can create a custom URL Scheme and add it to your Today Widget




Paste the below into the URL textbox and give it a name.

Cellular/Mobile Data:

prefs:root=MOBILE_DATA_SETTINGS_ID


This gets you to the "Mobile Data" section.

I'll see if there is a path to "Mobile Data Options" -> "Voice &amp; Data"



See this post: https://stackoverflow.com/q/8246070
You could try getting to the settings page for the network