3dx - Durability analysis on one part only in assembly

Hello,
I have an FEA structural analysis of an assembly of 3 parts over several load steps, only one of the parts is to be used in the subsequent Durability analysis.
Where in the 3dx environment may I define the scope of the fatigue analysis to be one specific part only? I would expect this control to be within the Mechanical Scenario module, but I don't see it there or elsewhere. Could a group perhaps be used to accomplish this?