Q.Kind of White Powder Under the Leaves of Green Pepper Plant
What is the name of the subject pest and how do I get rid of it?

Certified GKH Gardening Expert
White powdery growth on plants is generally associated with a fungal infection, namely powdery mildew, not pests. Here is an article or two on treating this problem that you may find helpful: https://www.gardeningknowhow.com/plant-problems/disease/get-the-cure-for-powdery-mildew.htm
https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm