Determine the stiffness matrix from FRF measurement

Hai, I am doing modal testing on aluminium plate. Impact hammer was used to excite the structure and single axis accelerometer was used to measured the response. Roving hammer technique was employed, where responses are measured from single references point and impact hammer was used to excite other points on the plate. Frequency Response Function FRF was plot by using PULSE Labshop and later curve fit by ME Scope. My problem now I do not have any idea how to get the stiffness and mass matrix from FRF that I had measured. Please, any helps are very much appreciated.