The input for this attack is up+right+square+triangle.
To make this easier for you, go to button configuration & set a free button to Lp+Rp.
Now go into arcade & just use Upright (Facing opponent) & whichever button you set Lp+Rp.
Once you land the attack 5 times its yours.
You can also just set up a 2 player battle & do the move against a dummy.