Hi in my iphone 12 sim network is not showing. Same sim card is working in other phone but in iPhone it's not working

Try first to optimize the range of the mobile network, see this Apple article:

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

If you see No Service or Searching on your iPhone or iPad - Apple Support

See this Apple articles below:

If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad

If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support

How to unlock your iPhone for use with a different carrier

How to unlock your iPhone for use with a different carrier - Apple Support

Manually update your carrier settings on your iPhone or iPad

Manually update your carrier settings on your iPhone or iPad - Apple Support

If you can't make or receive calls on your iPhone

If you can't make or receive calls on your iPhone - Apple Support