Battery health

you cannot do it manually. Only iPhone 11 had an auto recalibrate in iOS 14.something

It’s understandable that you’d want to know more about your Battery Health. 

Maximum battery capacity measures the device battery capacity relative to when it was new. A battery will have lower capacity as the battery chemically ages which may result in fewer hours of usage between charges. Depending upon the length of time between when the iPhone was made and when it is activated, your battery capacity may show as slightly less than 100%.

A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge. 

iPhone Battery and Performance 

General battery advice

Apple has recently updated the battery KB article, and it’s really quite good. iPhone Battery and Performance - Apple Support