Any solution for battery health decreasing on my iPhone?

Batteries degrade over time with usage due to chemical aging, that's just how they work.

You can expect about a 1% drop per month with average use on an iPhone.

This is an approximation, that is why it may be plus or minus a few percent on a month to month basis.

Apple recommends replacing it when it reaches 80%. To check your battery health, go to Settings > Battery > Battery Health.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support

About Lithium Ion Batteries

iPhone battery and performance - Apple Support (IN)

Here are some tips on maximizing battery life.

Batteries - Maximizing Performance - Apple

Yes, Battery Health decreases and will continue to decrease. Batteries are consumable parts and every time you charge your phone, its Battery Health will decrease. This is what batteries do. ALL BATTERIES. When your health dips to 80% or less (and it WILL dip to 80% or less) it will then be time to pay Apple to replace the battery in your iPhone. Until then, accept that Battery Health will decrease and that is normal, expected and cannot be stopped.