A. Quick Accept can be performed through the Calendar portlet.
B. Enable the Quick Accept preference under Setup > Activities > Calendar Preferences.
C. The Event record should be in Edit mode to perform Quick Accept.
D. The Quick Accept button provides users an option to mark events as Tentative or Accepted.
Explanation:
Reference: https://docs.oracle.com/cd/E60665_01/netsuitecs_gs/NSBSC/NSBSC.pdf