Cleo,
I'm not acquainted with your quad but I can tell you that having a bad motor in a new toy-grade drone is not uncommon. This is the inevitable result of mass-producing such tiny motors. I had that problem with my Syma x5c when I got it. Your options are to send the quad back to the vendor or to replace the motor, which is not difficult if you are capable of light soldering.
After replacing the bad motor my x5c has been performing admirably for more than a year after many crashes and being rain-drenched while stuck in a tree for two weeks. You might find that tinkering with these little helicopters is part of the fun. So give it a try. You can either buy motors or you can tell the dealer what happened and ask for a replacement motor.
Two of your quad's motors spin clockwise and two spin counter-clockwise. When you open the body you can tell which is which by the color of the wires and you will know which motor type you need.