Plug-in a second controller then go to the arena and on the first controller press to open the training menu. Now go to 'Select Sides' and move the second controller icon on to the same side as the first controller (which should be the attacking side). Now return to the training menu and choose 'Practice Set-Piece' and practice a corner with only a defending Goalkeeper, as many attackers as you want and playing as the attacking team. 1P and 2P will take it in turns to take the corner so make sure you are taking it with the controller of the account you want the achievement with before crying "Glitched Achievement". You also need to ensure that you cross to a 2P player and score with the 2P player. (2P assuming you want the achievement on the account that is using a 1P player).
You do not have to use a corner to get the achievement and you don't have to get it in a training match but it is the easier to get it in a training match and by using Corner practice it is less stressful because after every corner play the game will automatically set-up another corner for you, saving you the hassle of setting up a play manually.