Section numbering in book does not reset

Hi,

I have 10 seperate indesign files I am trying to combine into one book. The first number of the section number starts correctly in each page, but the second number is not reseting. 

For example, currently in file 1, the section numbers go 1.1, 1.2, 1.3, ..., 1.5

Afterwards in file 2, the section numbers go 2.6, 2.7, 2.8, ... 2.11 and then in 3, 3.12, 3.13, etc.

However, I want the section numbers to start at x.1 in each chapter. so in file 2, it should start at 2.1, 2.2, 2.3, etc..

Is this possible and how can I can this?

Thanks