There are a "veritable plethora" of web sources but I've no in-depth knowledge of any of them to be able to guide to specific ones that could recommend; take someone younger than I for that... :)
The documentation of Matlab is excellent and really helpful. Start to read here. To choose a matching lowpass filter, an analysis of the noise is useful, because there is an infinite set of different low pass filters. Choosing filter parameters requires to know, what you consider as signal and what as noise.
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