Ever since the Sony Z5 Sony has abandoned the fingerprint sensor on flagship handsets sold within the US. Recently though an investigation led to finding that the fingerprint sensor functionality had only been disabled through software limitations and the components needed for reading fingerprints are in fact still present.
If you own the Sony Xperia XZ or the X Compact it seems that you can flash software from another country to the device, for instance from the UK, to bring back the fingerprint scanner. Bear in mind that if you flash your handset you are breaking the warranty.
Should you want to you can flash the US software back and this means that the phone would be restored to factory conditions.
If you do want to go ahead and get the fingerprint scanner back you can check out the instructions of this link, but do you really want to relive that nightmare with your Sony Xperia XZ?