How can I design a suitable controller for this given system?

Question

How can I design a proportional controller to make closed loop transfer function stable? Parameter of the P controller is $$P[z]=K_P$$ Closed loop transfer function of the system is shown below. In this case the transfer function shown below must be made stable. $$\dfrac{K_PG[z]}{1+K_PG[z]}$$ $G[z]$ is the plant as can be seen from image. To make this system stable, we must find the values of $K_P$ that make the system is stable. Schematic of the system is shown below.