It's down the corridor where the toilets are by Athletes Foot shop and close to the info centre. Go to the bottom of the corridor and as the OP says - take the door on the left at the end and follow the corridor. He's good.
Ask at the information desk in ibn battuta. Not too sure of the exact location - if you are coming from the cinema end of the mall, its on the right hand side. You will pass aldo on the left, At customer service there he will tell you the exact door to go through. You go down the long passage, take the last door on the left and then straight in front of you is another door which is the tailor. It got a tiny sign on the door.