You can only engage Download mode from device powered off – hold Volume Down + Bixby + Power.
No problem – Easy Installer is generally fine if you have to start again. Rather than download again, Easy Installer will at first just verify the existing downloads.
I think this is critical … but
I think you will need to read some of the links already provided by @Lonad_West in his thread repeated here ! 
In general I would avoid taking advice / hints from the phone.