You can use the MODE SELECT xxx … command which would restrict the response to the set of modes limited by the command.
Please refer to the section 5.30.2 of the technical reference manual titled Mode Selection for more details on this command.
Also if you have the license for the advanced analysis engine, you can use the Ritz Vector Method of eigensolution as opposed to the default Subspace Iteration. This method is able to account for the dynamic loading and is able to extract the relevant modes that can have significant effect on the dynamic response. More details on that can be found at Technical Reference Manual section 1.18.3.1.2 titled Load-Dependent Ritz Vectors. The software can be instructed to use the Ritz Vector method of eigensolution by choosing the menu option Commands > Miscellaneous > Set Eigen Method > Load Dependent Ritz Vectors.