Go to the part you USED to go to 1099 MISC and then using the drop down menu THERE select "OMIT from 1099"  in every account you used for 1099s MISC before this year.  THEN SAVE.  Then go BACK OUT and BACK INTO 1099 NEC and the drop down menus will be unlocked from box 15.

THE PROBLEM IS YOUR SYSTEM IS LOCKED INTO THE "OLD" form and you have to OMIT the accounts there it INCLUDE it in the NEC form -- that is what is meant by UNMAPPING.