The white ring you refer to is just a plug retainer and has nothing to do with adjustment.

First, the most common problem is worn shift rod bushings. Check and replace, if needed.

If you noticed, the two holes in the switch that the mounting bolts go through are elongated for adjustment. Assuming the bushings are OK, with the selector in neutral on the shifter and the (metal) lever on the trans also in the neutral position, the switch needs to be adjusted by rotatiing at the slots to align the little black plastic rod on the switch to the metal arm with a pin through both into a hole in the trans body. Then tighten the two mounting bolts.

If all of the above are correct, it is either a wire problem or the switch itself. Both can be checked with a meter.