I’m not sure if you’re expected to take notes, so the following suggestions may not all be useful.

Saying “Could you please speak more slowly?” Will usually prompt people to slow down (and pay more attention to pronounciation) which means you can have a bit more time to take notes.
At the end of their explanation, if you are comfortable, you could ask them to reformulate briefly (in one of two sentences) what they said so that when you get a bit of time you can note that summary down and later go in more details.
Perhaps the least stressful option in terms of interaction would be to note down key words or doodle a concept in your binder so that later you can from these clues remember what you were told.

I hope this helped.