Well, i wanna flash 8.0 via dload but when i try forcing all 3 buttons it won't start updating android, it will enter in TWRP. Anyone know fix? 
You'll need to install the stock eRecovery first.
normally, erecovery should run parallel to twrp. when i use 3 button mode, erecovery starts. if i use vol+ & power button, twrp starts. maybe you release the 3 buttons to fast ? it take a very long time, starting erecovery. hold your 3 buttons 40 seconds! then u will normally enter EMUI install mode.can you tell me how to install stock eRecover ??