The 2D / 3D page can be found in the menu or by tapping the issues button on the bottom navigation bar.
Here is what the 2D / 3D page can look like:
Towards the top of the 2D / 3D page you see the issue board selector.
The issues that result from the filter on the chosen issue board are the issues who have their markers displayed in the 2D view.
On the upper half of the 2D / 3D page you will see the 3D viewer.
On the lower half of the 2D / 3D page you will see the 2D viewer.
Between the two viewers you will see a dividing slider
Drag on this slider to configure how big a part of the screen you want each of the viewers to take up