Some pressure switches are not adjustable. And a few brands/models use a pressure transducer integral to the machine's controller board instead of a separate switch.

Why are you trying to adjust the water level? Are you getting poor results? If so there are several other things you can try that would keep the machine operating as intended. I have seen those videos too and while a little increase doesn't hurt, some of them raised the water way too high, to the point of negatively impacting wash results and longevity of the machine.

Thanks for the responses. Yes, hvtech42, I feel that the little bit of water it uses is not enough for an effective wash. The clothes come out looking like they were rinsed but not truly cleaned.

I have no intention of going so far as some in the videos have. That said, a slight increase in water usage, IMO, would produce a better clean and would more effectively eliminate mid-range stains, which are not even dented right now. This particular machine sprays clothes and then agitates them while they are damp -- they don't sit in any kind of water during the wash cycle. I would like a just a bit of water in the drum whilst they wash.

If you have any advice or alternative solutions I'm open to them.

What temperature water are you washing them in? I get the best results with at least 100 degrees, and more if there is heavy staining.