Cross your cameras.

Convergence or toe-in in stereoscopic 3D camera systems is a term used to describe the inward rotation of one or both cameras along the vertical axis. When two stereoscopic cameras are converged on a subject, subsequent viewing of the recorded material will result in the subject appearing to be placed on the screen plane.

The terms is also (erroneously) used in post production to describe horizontal image translation (HIT). HIT manipulation can approximate on-set convergence. It is often used in conjunction with parallel camera recording for greater control over the final image.