“No system installed” is common for Xiaomi (and others ?), you can ignore it.
To install a new version if you have to modifed .zip at first install, do exactly the same :
- download to PC, edit .zip
- copy .zip to phone, anywhere visible in Files app
- boot recovery TWRP
- install (TWRP button), choose .zip (/sdcard or /data/sdcard), wipe Cache/Dalvik
- note : be sure to have TWRP ignore .zip signature