For MiFlash you have to download MIUI from official website (http://c.mi.com/miuidownload/index) then unzip the downloaded file in a folder on your computer then select the folder in MiFlash.
(it will reflash ALL the system, including recovery and boot partition and Fastboot in the latest version)
EDIT: Seems the latest version for libra is 0.7 and nougat, can you try to build a new version or maybe ask @Unknown to build ? Fastest and easiest guide for building unofficial /e/ rom
EDIT2: Lineage stopped supporting libra, idk if script provided by Unknown will work.