Aux repair or new stereo

Good evening. I have just bought a 56 plate roomster. I tried to connect to the aux but there is nothing under the aux cover looking under the centre console there is a cable connector( 1 cable looks pulled out.) Would this be easier to repair or install a single din stereo I already have at home. I'm not to handy with the electrical side and I know it needs a live feed to stop it being on permanently.