my battery health is 79%..Now what can i do?

Make an appointment (*) at an Apple Store or Authorized Service Provider, among this list:--> Apple – Location Selector , and have your battery replaced.

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.