You can apply for an extension on the module card itself, as shown in the screenshot:

You need to click on 'Get Extension', select the reason and confirm

(You should first open the module/assignment you want an extension in. Then click on the 'Get Extension' link.)

Click on the 'Get Extension' link before the soft deadline. If you need to avail an extension.

If you change your mind and plan to complete the module by the specified deadline. You cancel the extension request by clicking on 'Cancel Extension' link as shown in the below screenshot and then click on 'Confirm' to cancel it. Once you cancel the extension the original deadline will be shown as due date.