The position of bolt cutter blades can be adjusted using either the jaw adjustment bolts, located on the plate that is mounted across the two jaws, or the neck adjustment bolt, located near to where the blade joins the handle on one side of the tool.
(If your bolt cutters have two adjustment bolts, there will be one on each side.)
Both types of adjustment bolt are eccentric, that is they have an asymmetrically shaped shaft that is similar to a cam.
As a result, turning the bolt will cause part of the blade to either be pulled towards or pushed away from the joint, adjusting the gap between the blades, or the angle at which one of them is set.