My battery health is 88 percentage

88% is very good for a 5 year old phone. 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 24 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.

The absolute best way to improve the life of your battery long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the night the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern.

You have had it for 10 months. It was first released 5 years ago, and the last one came off the assembly line 2 years ago. So you do not have a new phone, or even a recently made phone. Your phone was 14 months old (or older) when you got it. You can find out its manufactured date from the serial number: https://beetstech.com/blog/decode-meaning-behind-apple-serial-number

iPhone 7 is a 5 year old phone.

My iPhone 8 is 4 years and I'm at 88%