How to set nextLaunch or date in API call to scheduled assignment workflow

i’m not sure if your comment relates to my query. There is no provisioning plan passed to the standard “scheduled assignment WF”. I am just trying to find if and how i can pass date as an input in my REST call to sailpoint standard WF “scheduled assignment” as i can’t see that as one of the WF inputs or can i create a request object using API call with a next launch date something like mentioned in my message below