I have a WX 251 Pro pressure tank. My cisteryn ran out of water and I think my pressure tank lost its prime. Not sure how to restore it.

I have a WX 251 Pro pressure tank. My cisteryn ran out of water and I think my pressure tank lost its prime. Not sure how to restore it. Pressure tanks don't lose prime. They are charged with air. Here's a diagram showing you the way a bladder, (not pressure) tank operates, (see image)
It's not the tank. It's either a faulty pump or the water table has fallen. Does your pump hold prime? If not can you prime it? Let me know, Tom

Tom is right. I really like that bladder tank pic he posts. Very useful

I would add that You are pumping from a cistern which ran dry so you lost prime. To reprime the pump, find the priming port (small threaded plug, or possibly a pressure gauge) on the pump's impeller cage. Remove plug and pour in water until it will not hold any more. It should hold that water without any leaking out the footvalve. If it does hold, then replace the plug and turn the pump on. Assuming you have water in your cistern again, you should be in business.