How do you convert 3 phase RMS line-line voltage to RMS line-neutral voltage on an unbalance system Basically how do you calculate using trig for all 3 phase?

The term, 'unbalanced system' refers to an unbalanced load. Under normal circumstances, an unbalanced load leads to unbalanced line currents. The line voltages are determined by the supply and remain symmetrical, even when the load is unbalanced. As your question refers to a 'line to neutral' voltage (i.e. a phase voltage), you must be referring to a star (wye) connected load, in which case the phase voltage (line to neutral voltage) is 0.577 (the reciprocal of the square-root of 3) times the line voltage (line to line voltage).