How can I use with mobile data

If you are asking about an IOS update, that has to be done using WiFi or a computer. From the article below.

You can update your iPhone, iPad, or iPod touch to the latest version of iOS or iPadOS wirelessly.* If you can't see the update on your device, you can update manually using your computer.

Update your iPhone, iPad, or iPod touch - Apple Support

Get help with over-the-air iOS updates          

Update – Can’t or can’t restore 

Have you tried using iTunes on a computer or Finder if running Catalina to do the update?

 Update software on iOS devices in iTunes on Mac

If you see an error when you update or restore your iPhone, iPad, or iPod      

See Update your carrier settings on your iPhone or iPad https://support.apple.com/en-us/HT201270

Also, see If you see No Service or Searching on your iPhone or iPad https://support.apple.com/en-us/HT201415

Update what?