I haven't installed this ROM yet mate..
But if there is indeed a system update option within the ROM then you can install that, don't reboot.
Open Magisk and click install after OTA.
If there is not a system update option. Then I could only assume that you would have to use TWRP to dirty flash the ROM or perform a clean install by wiping data in TWRP then flashing the ROM.
If that fails then a format and installation although I would assume that the latter is overkill and only necessary if there's a major issue with your installation.