It depends on the result you want.
If you are fitting a model, you have to specify the model, and then do the linear or nonlinear regression. Plot the model with the estimated parameters with your data.
Another option is the Savitzky-Golay filter. This is essentially a low-pass filter that can smooth the noise in your signal.
Otherwise, I would do a Fourier transform, find the most prominent frequency (or frequencies, depending on the information you want from your data), then use the Signal Processing Toolbox designfilt function to create a filter to pass your frequencies-of-interest. Then, plot the filtered signal with your data.
Use the hold function to plot more than one set of data on the same axes.
