You can design a lowpass Butterworth filter in runtime, using butter() function, and then apply that to the signal.
fc = 300; % Cut off frequency
fs = 1000; % Sampling rate
[b,a] = butter(6,fc/(fs/2)); % Butterworth filter of order 6
x = filter(b,a,signal); % Will be the filtered signal
Highpass and bandpass filters are also possible with this method. See https://www.mathworks.com/help/signal/ref/butter.html