Read here, you will get the answer. I expect some efforts from your side, lerning by doing is best way.
Case 1: if you want to supress all frequency more than 50Hz, its Low pass filter.
Case 2: If you want specific, supress the 50 Hz only (It can been done through Notch filter)
[b,a] = iircomb(cut_freq,input_signal,'notch');
Still, unable to solve it, let me know.