To change the IMEI number on an iPhone, you need to jailbreak the device. Jailbreaking allows you to gain root access to the iPhone's operating system, enabling you to install third-party apps, tweaks, and modifications not available through the App Store.
There is no reliable, software-only way to permanently change an iPhone's IMEI. Jailbreaking gives you access to system files, but the hardware-locked IMEI remains unchanged. 3. Why People Seek IMEI Changes
While jailbreaking removes software restrictions to allow customization, it does not grant access to rewrite the hardware-level identifiers on modern iPhones.
Changing the IMEI (International Mobile Equipment Identity) of an iPhone is through standard jailbreaking and is illegal in many jurisdictions. The Reality of IMEI Changing