Do you mean NG? NG+ is for completed save files like having all the power ups and all that
To reset though like have a fresh file go to your local disk (C:), program files, steam, steamapps, common, deadcore, then I'm not sure which of the sequence of numbers is the current save but you can either move them to your desktop to back them up or something or just delete it altogether if you want to start new
There is another solution created by "MrStandalone" which has changed the "Assembly-CSharp.dll" file simply press F3 to reset the save " and a lot of other things like pluggins management.
But it seems that it is deleting the file from its GitHub (https://github.com/MrStandalone). I will be able to send you the file once I have its authorization (or that it does him himself).
Edit : It seems that it is doing a file updated but I did not have time to look at it.