Choose the move tool
Select the layer to be rotated in the Layers panel.
Make sure the layer is not locked (right click layer -> make sure ‘Lock’ is unchecked).
In the transform panel, you will see a square with nine smaller squares.
Select one of the squares. This is the centre point, on which the rotation will be made. The centre square is a common choice.
Edit the Rotation value in the Transform panel. This is labelled R: . A positive value results in a clockwise rotation, and a negative value results in an anti-clockwise rotation.
The above steps will also work in Affinity Designer