Touch id is not working after screen replacement.

Then you are lucky the phone is not "bricked" and unusable! Back up your data ASAP!

Also bring the phone back to the technician that changed it as it is a hardware issue (incompatibility) with the new screen and the Touch Id; you cannot do anything by yourself or in software!

Hello! After a screen has been replaced, the Touch ID sensor is reset for security reasons. In order to enable it again, go to Settings > Touch ID and Passcode, and tap on Turn on Touch ID, or a similar button, and you will be asked to put your finger on the Touch ID sensor. Have a great day!

Where was the screen replacemend been done (official Apple Service) and is the part original or "some compatible" screen? What device do you have?