After you create a Task Card, you can edit it at anytime through it's details menu.
Step 1 — Locate a Task Card
On your Workflow page (or other Task-enabled pages), click on the Task Card.
Step 2 — Edit
In the window, click a text field and apply any necessary changes to the card.
Step 3 — Auto-saved
After updating the Task Card, simply click away or click the X and you'll see a "Saving..." notification appear to confirm your progress has been saved.