How could a plant control turgor pressure?

It requires water to do so. And for the uptake of water from it's surroundings, a cell must keep it's internal fluid or the cell sap at a higher solute concentration or lower water potential. This results in "endosmosis". Once water enters the cell, the protoplast swells and the cell membrane exerts a pushing force on the cell wall which is called the turgor pressure.

So basically, it has to regulate the flow of solute particles or ions across its cell membrane and keep its cell sap at a higher solute concentration or lower water potential, compared to its surrounding medium