If you calibrated your stereo camera, you should have the intrinsics K1, K2 for each camera, and the rotation R12 and translation t12 from the first to the second camera. From these, you can form the camera projection matrices P1 and P2 as follows:
P1 = K1 * [I3 | 0]
P2 = K2 * [R12 | t12]
Here, I3 is the 3x3 identity matrix, and the notation [R | t] means stacking R and t horizontally.
Then, you can use function triangulatePoints
(documentation), which implements the sparse stereo triangulation from the two camera matrices.
If you want dense triangulation or depthmap estimation, there are several functions for that. You first need to rectify the two images using stereoRectify
(documentation) and then perform stereo matching, for example using StereoBM
(documentation).