How to improve my battery health for my iphone 11 please help me

Your iPhone’s battery, just like any other battery, degrades in health as time elapses. You cannot improve the health.

Battery Health & Performance 

Your battery health is fine and is undergoing normal usage. Charge it whenever you want to. Try to not let your battery charge get below 20%. Your iPhone cannot be overcharged because it has a safety circuit built into it. You should change out the battery once your Battery Health reaches below 80% which will take over 2 years to reach under normal usage. Until then enjoy your iPhone.

Here is some more reading on an iPhone battery and its performance ➔ iPhone Battery and Performance - Apple Support

Axel F.