Excel if Statement replacing value in columns

I need some assistance with an if statement or a formula.

I have two columns K & L and both of them have values. If Column L has a value "X" I want Column K's value to be replaced with the one in Column L. However when there is no value in Column L, I want the value in Column K to remain as is.

Value in Column K to be replaced by the value in Column L only if available, if not leave it unchanged.