How do we replace iPhone 11 battery

Contact Apple or an Apple Authorized Service Providers. Newer models may have limited self-repair options, but any damage is the responsibility of the user who does it.

It really is not something for the average user to tackle.

Here is a link that will give you a bit more information. Let the PRO's at Apple do it.

iPhone Battery Replacement - Official Apple Support

Is battery rechanable. ?