1. Download ROM normaly(zip file)
2. Download payload-dumper-go( after unpacking the zip file on your pc you have to insert the file called " liblzma-5.dll " ) see any video on youtube or ask google.
3. From the zip file of your rom, extract the file called 'payload.bin' and transfer it to the folder where payload-dumper-go is located.
4.Now start CMD(command prompt) in that folder and write " payload-dumper-go payload.bin " and press Enter.
5. There it will create an extract folder and find the boot file. Transfer it to your phone, enter magisk and flash it through magisk.
6. When you flash it, a file named magisk_patched_******.img will appear in your Download folder (in phone).Transfer that to your pc.
7. Rename in magisk_patched.img and opet your platform tools file in your pc, move her inside. Again enter in cmd in platform-tools and write fastboot devices and
fastboot flash boot magisk_patched.img
Thats it


Sorry for my bad language, I tried my best.