How will battery health will up of iPhone will get up with battery health

You can't modify that value (unless your unidentified iPhone is a model 11, using this:--> About recalibration of battery health reporting in iOS 14.5 - Apple Support).

You can just use precautions in order to maximize performances.

See this article:--> Batteries - Maximizing Performance - Apple, and/or this user tip:--> https://discussions.apple.com/docs/DOC-9732

Regards

Giulio

It only goes down. Batteries do not have self-healing capability.