finding signals using peaks

I am having signal which have various peaks is there any function which can detect the peaks which repeat for a particullar time period let's say after 200 samples or after 2 seconds (Their amplitudes can differ in small amount) ?

[Rik]

You forgot to mention you don't appear to have the signal processing toolbox.

If you want to look at periodicity you could also consider Fourier transforms.

[Rohan Mehta]

How to use this fourier transforms ?

[Rik]

You mean this? https://www.google.com/search?q=how+to+use+fourier+transforms+in+matlab

If you don't have any clue what Fourier transforms are in the first place, I recommend you watch the videos on YouTube from 3Blue1Brown on this topic.