DISCLAIMER: I didn't come up with these steps, nor do I provide any support for these steps. I just wanted to add some additional information that helped me. Not responsible if you brick your phone/cause thermonuclear war/etc. Use at your own risk/PLEASE google/research if you are unsure of what you're doing.
Connect your phone to your computer via ADB. If you don't know how to do this, please search before following these steps
put stock boot.img into /sdcard/boot.img. MAKE SURE the name of the file is "boot.img", otherwise you will need to alter the following commands to use the name of the file. MAKE SURE your stock boot.img IS A VALID BOOT FILE, if it is not, Magisk will still restore the image, but the OTA will not work and your phone will not work upon reboot.