Download the zip for your device and unpack it to your computer.
Boot your phone into bootloader (volume down and plug in cable)
Type: fastboot flash ramdisk yourpatchedboot.img
Edit: if you have issues with Magisk and safetynet read
Like i wrote on p20 pro forum @LastStandingDroid you should include that here too..
After flashing the patched ramdisk they should install magisk over magisk manager again to pass safteynet and install modules.