Need help signal processing data from a 4DOF System in MATLAB

Need help doing signal processing on a 4DOF system; i already have all the data + mathematical model. Just need help processing it in Matlab to find the 4 natural frequencies of the system (I have code for this which isnt working properly atm), as well as using log dec. to find damping ratios of the system. Again, i already have all the data + mathematical model, just need help with processing the signal. attached is free body diagram of the 4dof system. need it done urgently and willing to pay extra if need be.