Related Questions:
I have Workflow steps that are Tasks, when do these appear in my Task List so that I can reassign them?
Why aren't my Workflow Tasks in my Task List?
Answer:
Workflow Task Steps get created as actual Tasks on the date you have set in the Workflow Step. This date is when the Workflow Step will run which in turn will create that Task and it will then be visible in your Task list.
Once the Workflow Step runs and the Task is created, you can then treat it as a regular Task and make any edits to it that you need to such as changing the assignee or adding reminders.