Unlike the 8 musical expressions (verlocity, length, octaves, pitch, strum, stutter, and 2 CC's), the grooves knobs follow both speed and loop length of the triggers.
The default value of a groove knob is zero, meaning no delay.
The range of a knob goes from zero till 100% delay.
Let's say that the tempo of the triggers is 16ths. If you set the second groove knob to 50%, the second trigger will be played at 16th+32th.
If you want a simple swing, just use two triggers, set the groove knob of the first trigger to zero, and the second to +/- halfway.
This results in a 33%-50% swing.