How can I practise questions I've previous got wrong or haven't yet seen?

Touch "Practise all questions" on the main Theory Test app menu:

Touch to select the categories from which you want to see questions, or touch "All categories" then touch "Start".

Check the type of questions selected - if not "Previously answered incorrectly" or "Questions not yet seen" tap the "Change" button to change that selection:

If there are insufficient questions "Previously answered incorrectly" or "Questions not yet seen" to fill the practice session additional questions will also be included.

Touch "Start Practise" to begin the practice session.