I inserted sim card but no service is showing
No service is showing while the sim card is inserted
No service is showing while the sim card is inserted
Note that a SIM won't work if your iPhone is locked to a different carrier. In that case, you would have to ask the carrier who holds the lock to release it. Which they might not choose to do.
How to unlock your iPhone for use with a different carrier - Apple Support
Contact your phone company (carrier).
If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support
I inserted sim card but no service is showing