The IMEI (International Mobile Equipment Identity) is a unique 15-digit identifier hardcoded into the device's hardware at the factory.
How to Change IMEI Number on iPhone: Everything you need to know
: Activation and network services are controlled by Apple’s activation database. Even if a local hardware change were attempted, the device would likely fail to activate once it connected to Apple's servers.
: Third-party tools claiming to "change" an IMEI are often fraudulent or only perform cosmetic changes to the software display, which will not bypass network blacklists or carrier locks. Alternatives and Related Procedures