First, you need to unlock the bootloader. (Not possible yet)
Install custom recovery (No unlock bootloader will not run)
Without unlocking the bootloader custom ROMs will not install.
Meizu locks all methods of unlocking, only modding the bootloader will work.
There is only one successful mod, it is unfortunately only for the m2 note. The m2 note: https://forum.xda-developers.com/meizu-mx/orig-development/tutorial-meizu-m2-note-bootloader-t3429843
The risk of modding is high as it may likely brick your phone.