How does the kinetic molecular theory account for gas pressure?

As the momentum of molecules is reversed during collisions with the walls of a container they exert a force on the wall. The net result of the force per unit area on the wall is pressure.

Note that the following is based upon a number of assumptions - the assumptions of kinetic theory,

Molecules move with constant velocity until they collide with the wall. During the collision their momentum perpendicular to the wall is reversed. From Newton's second law of motion a resultant force (acting on molecules) is necessary for that momentum reversal to have happened. The wall provides the force. From newton's third law of motion the molecule exerted a force on the wall.

The sum of all the forces exerted on the wall by all the molecules that collide at one time divided by the area of the wall gives a pressure on the wall - the pressure of the gas.