Revert to Samsung OS is easier using Odin than Heimdall, but you can follow
Flashing Samsung Firmware with Heimdall
or
[HOWTO] (Needs expert review) Flash Galaxy s9+ to Stock Android 10 using heimdall-gui
Revert to Samsung OS is easier using Odin than Heimdall, but you can follow
Flashing Samsung Firmware with Heimdall
or
[HOWTO] (Needs expert review) Flash Galaxy s9+ to Stock Android 10 using heimdall-gui