Never pour the isopropyl alcohol directly on the keyboard.

Lightly soak one end of a Q-tip in the isopropyl alcohol.

Clean the PCB keyboard by gently wiping the Q-tip along the surface.

Make sure that you are always working with an adequately clean Q-tip; change your Q-tip when it becomes too dirty. You may end up using 3 different Q-tips.

Take your time on this step. It is important that the PCB be as clean as possible!