To do this the Rubik's cube has to be solved.
Mu= move the middle piece up
The steps are all the same so do: Mu U
Now after you do that step 4 times in all, turn the whole cube down then left and do it again the pattern 4 times in all. Turn the whole cube down then left again and do the steps 4 more times.
Congratulations if you did it! If you didn't try again, don't give up. To fix it back to normal do the steps again.