My iPhone says no service after factory resting my other iPhone

I just reset one of my iPhone because I sold it

Did you follow the steps as described here in this Apple article? , see -> What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch

https://support.apple.com/en-us/HT201351

and now my other iPhone says no service

See this Apple articles below:

If you see No Service or Searching on your iPhone or iPad

https://support.apple.com/en-us/HT201415

Manually update your carrier settings on your iPhone or iPad

https://support.apple.com/en-us/HT201270

Set up cellular service on iPhone

https://support.apple.com/en-gb/guide/iphone/iph3f11fba92/ios