how can I add in or find device management in iphone x

Hi DarrenceC. Device Management appears near the end of Settings > General. You will only see Device Management if your device has been configured by your employer's MDM system. It does not appear on normal users' devices.

If someone told you to delete a Profile from your iPhone, look for Profiles near the end of Settings > General. If you don't see it, then you have no Profile. If that's not it, please explain why you are looking for Device Management.

What do you mean by device management? Is there a specific function you are looking for to turn on or off? Here is the user manual for iOS 11 and iPHone X -https://help.apple.com/iphone/11/

Device management would require an application such as Configurator 2 (available in the Mac App Store).