My iPhone has 82% battery health. What can I do to get the most battery life out of it?

You are fighting a losing battle here. The battery replacement is $89 in the US and nothing you do is going to help the inevitable. You will be much happier by just taking care of it now without having to jump through hoops just to make your device semi-usable.

iPhone Battery Repair & Replacement - Apple Support

My battery capacity was 96 but now it’s 82 what can do to bring it back to 96

You only have a few months left on your battery. When it gets down to 80%, make an appointment at the Apple Store or take the phone to an authorized Apple Service shop to have a new battery installed. About $89 U.S.

Find authorized service locations using the link just below.

https://locate.apple.com/

Maximum Capacity only declines. When the battery is down to 80%, it is time to replace the battery.

When you have a new battery installed in your phone, the Maximum Capacity will be 100% and start to decline again at a rate of about 1% a month on average.

This question is like asking my gas tank in my car is at 25%, how do I get it full again? And the answer is you buy gas to fill your tank. The same is true of a battery. When its capacity declines to a too low level, you get the battery replaced. ALL batteries lose their capacity to hold the same charge as new. They cannot have their capacity increased.

soliana ~

Batteries - Maximizing Performance - Apple

...Found by searching Apple's Knowledge Base.

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My battery capacity was 96 but now it’s 82 what can do to bring it back to 96

We already answered your question above. There is nothing that you can do.

Replace the battery when the Battery Health / Maximum Capacity is down to 80%