I want my battery to be 100

Batteries are consumable parts. Meaning every time you charge the battery, it loses a little bit of its ability to hold the same charge as new. And the more you use the phone and the more you charge the phone, Battery Health will decline. This is what batteries do. ALL BATTERIES. There is no way to restore a battery to brand new condition, once it has declined. So, you're asking for something which isn't possible at all.

Once the health of your battery declines to 80% or less, which if you own it long enough, it is guaranteed to do, you pay Apple to put a new battery in your iPhone.

Then, you will need to install a new battery in your phone. The battery will stay at 100% for 1 or 2 months, and then begin to decline about 1% a month after that.