The short answer: You’ll need a TRS-TRS cable with disconnected Ring tip.
The TRS pinout for the LR-16:
T (tip): used for the input signal from the mixer to the LR-16
R (ring): used for the return signal from the LR-16 to the mixer
S (sleeve): common ground
Normally if you are use TRS –TRS cable you can use that with the mixer insert slot.
If you want to use the LR-16 from Balanced source or from TS source, you have to use a same type of cable TRS – TRS, but you must disconnect the R (ring) tip on any end of the cable