Power off your modem, remove the original SIM card, and insert a SIM card from a different network provider.
Many free downloadable "ZTE unlock calculators" on file-sharing sites are Trojan horses disguised as .exe files. A high-quality tool (usually provided by reputable DC-Unlocker, FuriousGold, or UCT) is digitally signed and safe. Power off your modem, remove the original SIM
A: No. ZTE phones use a different algorithm (usually 8-digit). Modem dongles use the 16-digit NCK code. Power off your modem