I'm jumping out of my skin because of an acquaintance with ADHD.. Is there any way to handle this? ㅠㅠ

I explained everything in detail during the meeting, but they were just doing their own thing.. Then they came back later and said something completely different.
I explained it all over again, and they seemed to understand at the time, but then a few days later, they ask questions as if they're hearing it for the very first time...
On top of that, they are so stubborn that they don't do as they're told.. and they don't even say thank you.
It's different from just being rude.
It's really exhausting ㅠㅠ