Around 20 minutes of the practical test is independent driving. You may follow a sat-nav provided by the examiner, or traffic signs. Taking a wrong turn is not an automatic fail — you are marked on how you drive, not on being a human compass.
If you lose the route, keep the car safe, look for somewhere lawful to turn, and wait for the examiner. Your instructor should practise both sat-nav and sign-following so neither is a surprise.