controlling Elechouse MP3 player with an external switch for handicapped access

My wife is a special needs teacher and her students are only capable of pressing a switch to control an MP3 player.
I have been soldering leads to the play/pause buttons of inexpensive mp3 players and it works fine but I am looking for something more robust and possibly able to program to play for a certain amount of seconds.
I have an Elechouse MP3 shield and have loaded an mp3 file which plays as it should.
What I am hoping to do is program the Arduino to Play/Pause from an external switch.
Can anyone tell me what code to add to the arduino sketch and what pins to use to send the Play/Pause command?
thanks

Can anyone tell me what code to add to the arduino sketch and what pins to use to send the Play/Pause command?

Not without seeing your sketch.