If you reach out to your local support organization, they can provide a tutorial. We cover this topic in the LMS Test.Lab Structural Testing course on the third day. You will need measured FRF data with at least 6 excitation locations (usually with an impact hammer) and 8-12 response locations measured with a triax accelerometer (24-36 total responses). It's important to choose excitation locations that excite all 6 rigid body modes (avoid locations that only excite translational modes and not rotational ones) and responses that capture them as well (avoid locations along centerlines for example). If you have extra data it helps, because based on the correlation of the excitation locations and responses you can decide to remove columns or rows of the FRF matrix it if it does not aid the analysis.