Your ability to deal with roundabouts is a measure of your ability to judge what the other traffic is doing and being able to safely blend in with it. To do this look early and make use of your MSM and PSL routines.
The examiner or the sat nav will give you plenty of notice of the roundabout and where they want you to go. Pay attention to the lines and signs. Your ability to look and plan ahead will make this easier.
The classic learner errors with this are trying to do everything at the last moment. By leaving it too late they miss something. So give yourself enough time.