If the tool refuses to work, try these legacy unlock methods:

: It typically only works on older iPhones (iPhone 5s through iPhone X) because it relies on hardware vulnerabilities that Apple eventually patched. Temporary Fix

to see if your phone is even eligible for an unlock before downloading risky software. Apple Support

Note that some software-based unlocks are "temporary," meaning the lock might return if you perform a full factory reset of the iOS software.

If you cannot find a trusted copy, do not download from generic EXE hosting sites. Instead, consider using the open-source alternative SAM Unlocker or Ultrasn0w with similar baseband patches.