After clicking on an asset press the E key to enter rotation mode. In rotation mode a sphere is displayed in the middle of the asset and by dragging you can rotate the asset in the specific direction.

By dragging the red, green and blue lines around the spherical gizmo you can rotate the asset in 3D space using the X, Y or Z axis as a pivot.

For example, by dragging the green line, you can perform a transverse/horizontal rotation with the Y axis as the pivot.