Changing an IMEI is illegal in many countries (e.g., the UK) and can lead to severe penalties or network blacklisting.

a lost IMEI to match the original sticker on the phone's box is a legitimate repair,

: Contact your original mobile carrier to request an unlock. If the device is out of contract, they often provide a Free Mobile Unlock Code Inputting Unlock Codes Android 13 & below *#3988691# to open the unlock interface. Android 14 *#*#39326#*#* *#*#39324#*#* to enter the code. Third-Party Services : Platforms like UnlockLocks Realme Network Unlock App

Mentioned as a solution for unblocking or repairing IMEIs when there is "no signal" on Realme devices. Key Features and Capabilities