How I can reset restriction key for iphone

If you have forgotten the Restrictions passcode, the only way to remove it is to restore the iPhone to factory and set it up as new. You cannot use a backup, as the backup contains the passcode and will only put it back on the phone. See this for additional information, Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

If you can't remember a restrictions passcode that you created on a previous version of iOS, or you forgot your Screen Time passcode, you need to erase your device, then set it up as new to remove the passcode. Restoring your device won't remove your old passcode.