What's a way to enlarge my breast without operation?

You can't: It's not possible (unless you plan on gaining a lot of weight).

Breast enlargement: Of course garments/bras can be used. There are several other techniques to enlarge the breast with breast implants being the most popular. Either saline or silicone implants can be used. Other methods include external expanders (brava device), or fat tranfer via grafts or flaps. A variety of hormones can be used but are generally used only for male to female transgender treatment.