Adjusting Air Pressure in Well Pressure tank
With the tank in the basement you will need a few extra psi to fully push all the water out.
Many pressure tanks are on the same level as the faucets. You can do it either way but remember you have 8-10’ column of water of back pressure so where you might be 2 psi below the cut in pressure with the additional water column pressure you may need to be just over the pressure to use the total volume of the pressure tank so 42 psi may be needed to get full draw down. Open the water spigot upstairs and add air , the difference of draining below and above is about 4 psi so take the tank to 42 psi with the upstairs faucet open if it holds your bladder or diaphragm is good. If the faucet starts blowing bubbles and you loose the air pressure at the tank it needs a new bladder or replaced.
In reality it’s not a big deal unless you have a small tank.