Heard sales manager talking to his team to wash their hands properly after using computer keyboard.

And here I'm sinking my face in both hands and occasionally covering my mouth with one hand and biting my finger tips sometimes.

Simply clean the keyboard with antibacterial wipes from time to time - more often when there's an elevated risk of infectious diseases around (flu season), Also the mouse. Also the desktop. Also wash your hands after bathroom trips.

This is hygiene 101. If you do that, then covering your mouth with your hands isn't a problem.