Steam vr black screen while execute command hmd mirror off,how can I turn on the mirror ?

while execute hmd mirror off command , I can not reopen mirror on mode ,I donot know how to do . I try hmd mirror on ,but that doest not work ,some body kown the command , please help . this trouble spent me one day time already .
thanks .

I can resume reopen mirror on mode in this command.

“hmd mirror 1”

Please try once!