Two of my parrot fish are sitting on the bottom of the tank
The PH is 7.4 and I don't know how to lower it could the fish be sitting on bottom because of this

You can buy drops to raise or lower your PH to a neuatral setting or to one the fish are comfortable with. Alkaline or acidic. Also it helps to use products like amocarb. It removes amonia from the water while you filter it.

No.

Your fish are sitting at the bottom because they are more then likely sick.

Get your water tested before you start messing with water chemistry. It could be a lot of things.

Ph can make the fish sick if it has been sitting at a dangerous level for too long.
As calif said, there are products the raise and lower ph levels. You can get them from pet stores. Bicarb soda makes water more alkaline, but to make it more acidic you will need to purchase a special product.
But also take into account what lucky said... there may be more going on here than you think and the fish might be sick for another reason.