Well, I have not found any Android Pie based custom ROM for the ZenFone 3 Laser (ZC551KL).
I will update this thread once I come across anything.
To install a custom ROM you don’t have to ROOT.
You have unlock the bootloader on the Zenfone 3 Laser, then install a TWRP recovery available for your device.
Using the TWRP you can install the custom ROM then.
? GCam APK | LineageOS