my maximum health capacity is 84% what should i do???

What version of iPhone, and how old is it? You can set up a Genius Bar appointment to see about a battery replacement if you wish, but Apple generally says that if the device is reporting more than 80%, then the battery is okay. However the battery replacement program allows for replacements at the customer's discretion. See this, A Message to Our Customers - Apple There is a cost involved unless your device is less than one year old.

You can visit an Authorized Apple Service Provider or Apple Store next to your place and let them test the battery. As far as I remember, Apple usually replaces the battery when it reaches less than 80% capacity.

Some counterfeit and third party power adapters and batteries may not be designed properly and could result in safety issues. To ensure you receive a genuine Apple battery during a battery replacement, we recommend visiting an Apple Store or Apple Authorized Service Provider. If you need a replacement adapter to charge your Apple device, we recommend getting an Apple power adapter.

Also non-genuine replacement displays may have compromised visual quality and may fail to work correctly. Apple-certified screen repairs are performed by trusted experts who use genuine Apple parts.

copied from: Official Apple Support