LN is the ratio between the magnetizing inductance and the resonant inductance.
QE is the quality factor of the resonant tank.
In this equation, RE is the equivalent load resistance.
Selecting LN and QE values should result in an LLC gain curve, that intersects with MG(min) and MG(max) traces. The peak gain of the resulting curve should be larger than MG(max). Details of how to select LN and QE are not discussed here. They are available in the UCC25640x Design Calculator.
In this case, the selected LN and QE values are: