How can you rotate an assembly that has gotten out of level in one or more x,y or z axis?
right click your assembly and choose move with triad.
You can mate it to the main axis.
I will go with Rob "Mate the assembly" so that you know how much to move and if in near future you want to change the values/distance, you can easily do that via editing mates.
Allowing an assembly to float is most undesirable. It should be mated to either a fixed component or to the primary planes. Mating will reorient it parallel/perpendicular to the axes, as you want.
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