Increasing your tire pressure on your vehicle or trailer doesn't increase your towing capacity and so you would not gain anything by increasing your tires air pressure.
I would just keep the air pressure in your tires at the proper recommended air pressure to avoid any overheating of the tires or possible blowouts.
Just keep the air pressure in your tow vehicles tires and your trailer vehicle tires at the recommend and proper pressure and you should be just fine.
Just make sure that your vehicle can tow the heavy load and that you have electric brakes on the vehicle and trailer if you have a heavy enough load.
But adding additional air pressure to your tires will not do anything or increase your tow capacity and it may actually cause the load to ride rough or cause a blowout.