Rather than even trying to explain it, if you have the option, demonstrate it.
It is much easier, if there is a help desk with a live person, or someone from the IT department who is there live, to understand what's wrong when they can actually see what you can't do.
Ideally, if the situation presents itself, first have them do "the sighted way" what you are about to attempt to do, then do it with a screen reader until "the sticking point" is reached. That gives them an even better idea of where the issue is and why it needs to be addressed.
Trying to describe accessibility, or the lack thereof, in the abstract is very, very difficult indeed. But it's very simple to demonstrate it, even if that ends up being via video screen capture.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
The poor wish to be rich, the rich wish to be happy, the single wish to be married, and the married wish to be dead.
~ Ann Landers