You will lose internet connectivity until you re-enter ISP-specific settings (PPPoE username/password, VLAN ID). If you don’t have those, call your ISP before resetting.
For new ZTE routers with (remote ISP management), your ISP can change your admin password without notice. If you find your credentials suddenly stop working, your ISP likely pushed a config update. You may need to request the new password or factory reset and immediately disable TR-069 (if allowed). zte wifi router login