how to fix my iphone battary health?

You can not raise your battery health. It is typical to lose 2% or 3% within the first few months and it will level off after that. - iPhone Battery and Performance - Apple Support

debjyoti241 wrote:

Actually am using iPhone se2,i am not using heavily but my i phone decreased battery health to 97% and I realised am lost 30min less battery backup...how to fix it?

Batteries are consumables; they lose a little capacity every time they are discharged, then recharged. On average this works out to about a 1% loss for every 25 “full charge cycles”. As one example, if you charge the phone overnight, every night (and that is what you should do; it is a best practice), it starts the day at 100%. If it drops to 20% by the end of the day before you charge it again overnight that counts as 0.8 full charge cycles (20% to 100%), or about 25 full charge cycles per month of use. For this example your battery capacity will lose about 1% per month. Of course, if the end-of-day level is higher than 20% the capacity loss will be a little less, and if it is lower than 20%, or you charge it during the day, the capacity loss will be higher.