I can't find the devices and profile management in my iPhone

Did you buy this iPhone used?

You can use the search field at the top of settings to look for the Profile.

Just type "Profile" in the search field and it should find the Beta profile.

After that follow the steps here to remove the Beta form your iPhone and restore to a non-beta iOS version.

How to install or uninstall iOS beta software - Apple Support

Did you sign up for the beta program?

If you're looking under settings, general and you don't see profiles, then you don't have one installed on your device.

I have no apparent profiles but on my new phone it says there is a IOS 11 beta 9 ready to install?