Fingerprint doesn’t want to activate on my iPhone

Start with this Apple support article—>If Touch ID isn't working on your iPhone or iPad - Apple Support

If this doesn’t solve the problem post back with more details about your phone.

One important question: Does your phone have the original screen, or was it replaced by someone other than Apple?

That's why it will never work again.

You should have used an authorized Apple repair location.

It is possible to replace the screen without disabling touch ID. Apparently the certain technician did not have the skill to do that.