How do I pressurize an old tank with no air valve m
Drain it, then turn on the pump.
Old tanks had no bladder, so the air and water are not separated. As a result, there's no pre-pressurization, and the size of tank needed for the same effect is considerably larger. A properly set up and maintained system also has a (prone to fail) widget that adds air to the water coming from the well, since the air in the tank will dissolve into the water in the tank over time and make the system "waterlogged" causing short-cyling of the pump - requiring draining the tank again. If the widget is working right that's less prone to happen, since more air is added each time water is pumped.
Lived through it growing up, purchased a bladder type tank without batting an eyelash when the time came to set up my own well. But if you are not yet at the stage of fixing/upgrading the system, simply draining the tank before you start pumping water is what you do.