I have visited at Service Center they only downgrade the OS in Nogut . Also they didn't informed to me that i have to unregister from Beta Lab.
The care center will not be able to roll you back in the appropriate way for beta labs.
To roll back, you can simply go to https://www.nokia.com/en_int/phones/betalabs, scroll down to "Want to roll-back?", then select "Roll back via OTA". Remember to read the instructions before you request the roll-back.
You do not have to unregister from beta labs to revert back to Nougat.
Hope this helps.
Have a great day!