I want to manually set the time zone on my iPhone. But the setting for this says “The time zone cannot be set manually due to device restriction”.

I want to manually set the time zone on my iPhone.  But the setting for this says “The time zone cannot be set manually due to device restriction”.  

A previous answer to this question said, as below, change your restrictions.  But it is not clear from the link where to do that.  Can you explain exactly where I can change the device restrictions to allow me to change the time zone manually?   I manage my iPhone, it is not under anyone else’s management.  

The previous answer which does not answer the question clearly enough for me; “we also see from your screenshot that your device has restrictions enabled, preventing you from manually adjusting the time zone. If your device is not managed by anyone other than yourself, you can disable restrictions following the information in Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support.”