How to turn back to iOS on my iPhone 14 Pro from 16.6 back.

Apple does not support downgrading iOS or iPadOS unless it is a beta version of software.

Apple provides these instructions on how to uninstall iOS beta software; click here —> How to uninstall iOS or iPadOS beta software - Apple Support

K-x-B-1 Said:

"How can I turn back my iOS on my iPhone 14 Pro right now it’s running 16.6 and I would like to go to an earlier version."

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Downgrading the iOS:

You Can't. So, to troubleshooting things a little further, why do you want to downgrade the iOS? Is there something not working correctly, or is there a setting you do not like?

That is not possible, Apple doesn't allow downgrading of the operating system.

”K-x-B-1 Said:

"How can I turn back my iOS on my iPhone 14 Pro right now it’s running 16.6 and I would like to go to an earlier version.: All of above”

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Provide Apple Feedback of your Opinions:

Do your Part: Provide Apple with feedback on this, letting them know about you options.  Apple may not get back to you directly, but the more feedback they receive on this, the more they will know what issues have come about, and what changes and bug fixes include in updates to come.

1. Go Here: Feedback - iPhone - Apple
2. Select: "Performance" for the "Feedback Type"
3. Comment: on your opinions of iOS6.6. Include the URL of this thread.
4. Proceed from there as necessary

Be respectfully of how you word it, or it may be blown off.