Sending a 'Morphtronic' monster to the GY is a cost to activate "Morphtronic Repair Unit". The effect targets 1 'Morphtronic' monster in your GY.
There must be a 'Morphtronic' monster in your GY in order to activate "Morphtronic Repair Unit". However, as long as there is an eligible target in your GY, you can send a 'Morphtronic' monster from your hand to the GY, and then target the monster you just sent. If there are no 'Morphtronic' monsters in your GY, you cannot do this.