Things change, and sometimes the Card completion date your Manager originally assigned is no longer achievable. You can request an extension any time by expanding your Card's header and selecting Extend.
In the popup window, you can add a note to your Manager (perhaps the reason for your request?) as well as propose a new completion date.
Until your Manager approves or rejects the extension request, your Card's badge will have a small blue calendar icon attached to it.
If your Manager approves the request, the Progress Dial will show the new completion date.
If your Manager rejects the request, the date will remain as before. You can always ask again - maybe your Manager will be in a better mood next time?
In most Teams, someone else will be your Manager. But in some Teams, you'll act as your own Manager. In those cases, any enrollment requests you make, including extensions, will be automatically approved. In the Pract.us Public Team, which everyone is a member of, you are your own Manager.