The first method:

1-First select your own suitable size, then click: ADD TO CART

2-Click: VIEW CART

3-Swipe down to appear: COUPON

4-Fill in the discount code: CH, then click: CHECK OUT

5-Discount code successfully used

 The second method

1-First select your own suitable size, then click: ADD TO CART2-Click: CHECK OUT

3-Click where the red arrow points.

4-Enter the discount code: CH and click where the red arrow points

5-Discount code used successfully