You needn't pay a tailor to make this most basic repair. Hold the button in place, and send the needle from the back of fabric up through one of the holes.
Place a toothpick over the button, then stitch down over the toothpick, into the next hole. Stitch until each set of holes has been bound five or six times.
With needle and thread between fabric and button, remove the toothpick. Lift up the button, and wrap the thread around the exposed threads between the fabric and button several times. Tie off the thread under the button, and trim excess.