Download ASUS Flashtool 1.0.0.45 for Windows
ASUS Flashtool is a program for flashing ASUS Device, including Zenfone 3 series. In ASUS Flashtool 1.0.0.45 have more supported device. To perform ASUS flashtool you need RAW firmware.
A400CG, A450CG, A500CG, A501CG, A502CG, A500KL, A600CG, A601CG, Z170C, Z170CG, Z370C, Z370CG, Z580C, Z580CA, Z451CG, ZE500CL, ZE500KG, ZE500KL, ZE550ML, ZE551ML, ZC451CG, ZC550KL, ZC551KL, ZD551KL, ZE500KG, ZE500KL, ZE520KL, ZE550KL, ZE552KL, ZE550KG, ZE600KL, ZE601KL, ZS550KL, ZS570KL, ZT500KL, ZT581KL, ZX551ML
How to Use ASUS Flash tool can be read Here : https://azus-zenfone.blogspot.co.id/2014/09/asus-flashtool-installer-for-zenfone.html