Here is another tutorial for unlocking your bootloader in Asus Zenfone 2 laser 5.5s ZE550KL asus_Z00LD device for you to be able to flash TWRP and make a stock rom backup to your device to restore it later if you will encounter any issues like boot loop or stuck at Asus logo later on.
For this device you need to have root access to unlock its bootloader.
If you happen not to root yet your device you may wish to visit my post here.
Let me show you how to root your Asus Zenfone 2 Laser 5.5s (ZE550KL) Lollipop version with just the use of one simple tool which I have tested myself. If your device is with the marshmallow firmware, please downgrade first to a lower version such as lollipop since the app won't be able to root your device. Try to check from time to time if the developer of this app have included marshmallow devices already.