I’m not able to use Face ID after changing the back glass

Get support now by phone or chat,

set up a repair, and more.

• Call Apple Support at 1-800-APLCARE.
• International Support.
• Contact Apple Support.
• Chat using Messages.

The back glass on an iPhone 11 I not replaceable. Your phone is unsupportable now that it's been tampered with.

You will either have to live with it as is or buy a new phone. Apple won't touch it.