How can I find out which app drains my iPhone battery?

What do you mean by "reset" your battery life?

If your battery has drained, you "reset" it by recharging it.

If you mean that your maximum capacity in Settings>Battery>Battery Health is dropping, no, you can't.

You can try force quitting the app to see if that helps.

Close an app on your iPhone or iPod touch - Apple Support

If that doesn't help, try deleting the app and re-installing it.

Certain types of apps will tend to drain your battery charge faster than others. Especially graphics-hungry games.