Locate the fine adjustment nut of brake at the right hand side near rear wheel of your bike. Rotate the adjustment nuts slowly in clockwise direction to tighten and anti-clockwise to loose the brake.
Once you have rotated the nut, check the tightness at the brake lever by pressing it down.
If require, repeat the step 1 and 2 till you get proper breaking adjustment.
If there is no improvement at braking condition, or if you are facing any similar issue or bike service, please do contact your next door Doers certified mechanic for service.