How do I recharge this pressure pump?
To borrow what User58220 said, I think part of your problem here is that you have the wrong pump for your application. This pump is designed to boost the incoming water pressure from a municipal water service. It requires a minimum of 10 psi to function correctly. The rule of thumb is 1 psi for every 2 feet of elevation, so you will need to elevate your tank at least 20 feet above the pump. If you can't, then hire a competent plumber to install the proper type of pump.

Provided you do have at least 10 psi, next you should check the controller. Hold the square button down until the display says Lo. Make a note of the number that appears after a few seconds. Press the square button twice. It will either display an error code or --. Consult the manual if you have an error.

The final thing to check is the pressure tank. Turn off the pump, turn off the water from the tank, and open (and leave open) a faucet to relieve the pressure. Then find the air stem (should look like the fill valve on a tire) and read the pressure. This number should be about 2 psi less than the Lo number you noted previously. If the pressure is incorrect, then let some air out or pump some air in until you are 2 psi below the Lo number.

If the tank leaks water out of the air stem when you try to take a pressure reading, then the pressure bladder in the tank is ruptured or water-logged. Replace the tank.