My hot water tank is made by Rheem. Model: PVS180. The pressure switch fails to open.

If the switch is defective replace it.

If the switch is defective replace it.

Please tell me how I can replace and adjust it?

Please tell me how I can replace and adjust it?

If you do not have the mechanical skill to test and replace the switch then you should not be messing with it. It is really quite simple. Secure the heater then remove the defective part and replace. Sorry but a step by stem would take hours of my time trying to type it all out. I would go to the water heaters manufacturing site and locate a service manual for your unit. All the repair steps are in the manual. I do not have that manual so I cannot send or post it here.