How do I amend just my state 2020 return?

Yes, you can amend your state return only. Please see I need to amend my state return for instructions.

Please wait until your state return has been processed before filing the amended state. Please be aware that you can e-file your 2020 amended federal tax return, but most states require amendments to be printed and filed by mail.

This option is not working for me. It keeps coming to turbo tax is waiting guidance or something from the IRS. I do not need to amend my federal only my state. Why can't I do that?

Until the amendment program is once again operational you will either need to wait  or  use paper forms.  You have  3 years to amend a return so I would suggest just waiting.  

When amending my CO state return, I attempt to edit Enterprise Zone Credits but the changes I make will not save/stick.  I uncheck all boxes and check 'None of the above apply to me'.  But the credit remains and when I try to Edit again the original box is checked.

At this point, I would suggest deleting Colorado State Form DR 1366 to see if this will alleviate your dilemma. If i Turbo Tax online:

1. Go to tax tools>tools>delete a form
2. Look in your list of Colorado forms and delete DR 1366. If you are using the desktop software,
3. Go to the forms mode in your return and look for Colorado Form DR 1366. 
4. Select it and on the right side of your screen, delete the form at the bottom.