That is the power steering belt. At the location where your finger is, there is a bolt behind the pulley. You need to turn the pulley until the service hold on the pulley lines up with the bolt to loosen it. this bolt is the adjuster and directly below it under the pump, there is another bolt for the pivot. It has a second bolt at rear of pump.

For adjuster bolt, loosen at least 3 turns of the bolt whereas for the pivot bolts, loosening them 1 turn should be sufficient for you to push th pump inwards to gain the slack for removing/installing the belt. Remember to loop in the alternator belt first, that is the innermost belt on the crank pulley and turns the alternator and water pump pulley (onto which the power steering pump belt is mounted).