Retrieving intrinsic matrix from two stereo depth sensor that resulted in a single depth image

Question

I have one stereo camera that outputs the depth and RGB images. I have retrieved the distortion and camera matrix using the checkered board(intrinsic matrix for RGB camera). However, in the above discussion it seems like we need the depth sensor intrinsic matrix too to align RGB and depth image together. I have worked with retrieving RGB camera matrix but not the depth sensor when my two depth sensors are providing me with one depth image. I would like to have some insights regarding the above question, as I am stuck with how do I proceed further.