Getting +/- voltage from a benchtop power supply
Your power supply unit contains 2 independent power supplies.  Each one has a ground, + and - terminals.  To get +12 volts from one, connect the ground and - terminals together and then hook the + terminal to where your circuit needs +12 volts and hook the - terminal to where your circuit needs the +12 volt return.  On the 2nd power supply on your unit, connect the ground terminal to the + terminal.  Now connect the - terminal to where your circuit needs -12 volts and hook the + terminal to where your circuit needs the -12 volt return. If you set your supply unit to the master/slave mode, then you need only adjust the master supply to 12 volts and the other (slave) supply will automatically follow.  Otherwise, you can set them separately if you prefer.