Results:  I copied the client  in question, removed the current year's information and entered the prospective information for 2021.  This gave me new tax results for a preview of 2021.  However, I don't know if it accurately accounted for "loss carry forward" after 2020 use of same or if it assumed 2020 loss carry forward.  

When I closed the system and reopened, the 2020 client number was changed to the preview client number and it appeared the system assumed that the preview was now the 2020 return.  I renewed all 2020 information and restored the 2020 return.  The preview return had assumed the client number of the original return and would not show the return until I paid an additional fee, which I didn't.  I then deleted the preview return and everything was restored to normal.  

Unfortunately this solution didn't accomplish my intent since I'm unclear on how the system handled the loss carry forward.

Thanks for your help.

Mike D.