There is a command for that: Shift + G. The percentage of swing is editable by double-clicking on the word, "Swing". What is not currently working well is to set limits for the rhythmic values affect by swing - if you set eighth notes to swing, 16th notes also swing by default. That's not correct behavior. I would ask Presonus to correct the behavior of the Swing function. But, in the meantime, swing does basically work and there's an easy way to implement it.