Tapping the Map Orientation button steps through the different orientation modes available:

Free rotation Use your pinch/zoom gesture but rotate the gesture to rotate the map
North up Locks the map with magnetic north at the top of the screen
Planned track up Keeps the current leg of your flight plan straight up and down the map
Track up Keeps the aircraft icon pointed to the top of the screen

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Help Centre (Tap and hold to open the Link)

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