1. Download room
2. Turn on newest TWRP
3. CLEAN> ADVANCED>DATA, CACHE,SYSTEM, DALVIK (NO INTERNAL)
4. GO TO INSTALL AND SELECT ROOM
5. AFTER INSTALING ALSO CLRAN DALVIK
6. REBOOT TO SYSTEM AND WIAT ABOUT 4 MINUTES...
DONE, YOU HAVE ANDROID P ON MI 8