Hi Belma,PnP is designed so a default router/switch out of box can contact PnP server without any user input on device side.  There is a test command "test pnp discovery process".  But this is only for debugging purpose.

PnP discovery will not initiate if there is existing configuration on your switch.  1N missing is a typo.  For more detail, check solution guide: Solution Guide for Cisco Network Plug and Play - CiscoFirst section of option 43 string: ■5A1N;—Specifie...

Your DHCP server setup has both DNS and Option 43 configs.  When your 3850 booted, there will be two discovery methods competing with each other.  In your case, DNS was able to resolve devicehelper.cisco.com first before Option 43. Try to remove " dn...