In order for this to work, your opponent must be in a powerplay.

You have to press Y to initiate a fight. Try to get a fight when your opponent has 20 seconds or less on their powerplay.

After your fight, your opponent's powerplay will be done( but your player will not leave the box until his penalty time expires).

When your player's penalty is over, then you will get a powerplay.

The time depends of how much penalty time your opponent took.

For example your opponent has 1:10 left on their powerplay and you start a fight, your powerplay time will be 50 seconds.

Be careful though, sometimes you might get called a penalty for slashing.