Re-flash FairPhone 3 back to Stock ROM/Original OS

[HOWTO] revert your Fairphone 3 with /e/-OS back to Stock ROM using Debian based GNU/Linux
Mission: To revert back to original or stock ROM provided by OEM for your Fairphone 3 smartphone. Prerequisites: A Fairphone 3 smartphone running /e/OS with complete backup of important data on a PC or an external drive or source. Downloaded copy of latest stock ROM from AndroidFIleHost here. (For…