Final answer:
Rotating a whole assembly by 90 degrees involves selecting the assembly in a CAD program, using the rotate tool, specifying the rotation axis, and manually entering the required degree of rotation.
Step-by-step explanation:
To rotate a whole assembly by 90 degrees, you would typically use a software tool within a Computer-Aided Design (CAD) program. The specific steps can vary depending on the software you're using, but the general process involves selecting the assembly, choosing the rotate tool, specifying the axis of rotation, and entering the degree of rotation which is 90 degrees in this case. In most CAD programs, you can either manually enter the rotation value or use a rotation handle to visually orient the assembly to the desired position. Always remember to save your work after making transformations to avoid losing data.