HELP with low pass filter (FIR)

Hey guys, I'm new on Matlab and I have no idea how can I do a low pass filtre to filtre my Audio file. here is my Audio file to complete my Project i did everything in the project i am stuck in this step, i would appriciat the help and i want to learn how not just copy past the code and thank you so much for the help

Here is Professor Dorr ComputeFreqResp.mcd script that need to be modified but i dont know how