Unable to complete Touch ID please go back & try again. How can I solve it?

That is usually a hardware problem. If you have had the screen replaced by anyone other than Apple that will permanently break TouchID. If it is the original screen, or if Apple replaced it, contact Apple to discuss repair options.

Apple’s formal support can be reached several ways:

• Click on “Support” at the top of this page
• Go to Contact Official Apple Support

Note that both of the above have options to receive a callback or chat

• Install the Apple Support app on your phone from the App Store and use it’s contact feature.

What did you learn from reading my post that you just responded to?

Everything you need to know has already been posted in this thread. There is no further advice that anyone can give you.