To access the Polar symmetry tool select the compass symbol in the right top corner and then select Polar Symmetry at the bottom of the sketch.
This tool can be used by sliding the white circle up to the amount of polar symmetry you would like. You should see the bar go purple which is how you can know it is active. The axis of your polar symmetry in the centre of the screen can be seen as a light grey line.
Set the axis
The button to the right of the polar symmetry slider can change the way the axis lies. This will always be in the centre of the screen.