Here's how to rotate a model:
Select the model in the object list and make it visible in the scene by clicking on the eye icon. If you don't see the model in the scene, click on the Focus icon.
Switch to Perspective view as it is easier to rotate your model in this view.
Click on the Rotation tool. The tool displays a circular rotation gizmo indicating the axes along which the model can be rotated. To lock the rotation to 90 degrees, press the Shift key and drag in a circle to rotate the model perpendicular to the current axis.
Right-clicking on the model provides several options:
Set Pivot Point
This option allows you to determine the center point of rotation. Right-click on a point in the model and select Set Pivot Point.
Center Pivot Point
This option centers the pivot point in the model.
Reset Rotation
This option resets the rotation to the state the model had when it was uploaded.
Snap to Orthogonal
Check this option to rotate the model only orthogonally. The shortcut for this option is holding down the Shift key.
Rotate the model to the desired orientation and save by right-clicking outside of the model.