I am 21 year old girl. Can I increase my height?

Unlikely. The major driver for height originates in the long bones of the body, primarily the legs. When the growth centers of the legs have quit making new bone, as would be expected by 16-17y in a female, you're as tall as you will ever be. An x-ray if the hand can be used to demonstrate you're bone maturity & if the growth centers show open growth centers you may grow taller.If not you, re done.