Do I have to change the battery if its health is at 99%?

Stop watching Battery Health. It will drive you crazy. If you are that upset over a 1% drop in a week, you will go crazy. Check it only if you experience a problem with the battery. Check it around 6 months, then 8 months. If you get below 80%, then you need a battery replacement, but you certainly don't need one at 99%. It should only be checked if the battery appears to be having a problem charging.

There is nothing wrong with a battery at 99% battery health. That is almost perfect unused. Why would you think you think you need to change battery. Apple does not replace batteries until they are below 80% health.

You're welcome.