How to I put my battery health back to 100

You cannot put Battery Health back to 100% as all batteries deplete with time. You have not mentioned what your Battery Health figure is, but you need not worry until it reaches 80%, at which time you will need to make an appointment at the nearest Apple Store for a Battery Replacement. Check this link...

Batteries - Maximizing Performance - Apple

You cannot raise your battery health. You have not shared your battery health, but I would assume, being an iPhone 11, that you have a healthy battery. There is no need to worry until it gets just above 80%. Once it reaches 80%, then you need to replace the phone, or the battery. Please leave the battery replacement to a professional.

now, if you need a professional to buy a phone for you then…

You can't. As you use the phone batteries wear out.