To all the boys I loved before- read continuation or beginning?

The book "To all the Boys I loved before" by Jenny Han has already been filmed (Netflix). However, there are 2 more parts of the book.

I would like to know how the story goes on and consider buying the books, but I do not know if I should start with the first part (which I already saw on Netflix) or start with the second part, because I already know the story of the first part?

So I should read through the first book anyway, or is it enough if I continue with the second? Have all important actions been given again?

I would read the 1st Already, as there are of course modifications. In addition, the book is really good, even if you know the story itself.