I recently went to an event that was really inaccessible, but didn't have to be. Through my frustration at not being able to do anything about it, I've realized that as a presenter at conferences or leader of events, I can make this better. At the very beginning I will say something like:
"Before I get started I want to make a request. If at any point there is something I can do to make this more accessible for you -- like if you need me to face you when speaking, or to repeat or explain something, or to wait a minute so you can make a note or handle a potential trigger -- please interrupt me with a signal like raising your hand or saying 'pause.' It is important to me that I not accidentally exclude people, so if you're up to it, please point out any way I can be more inclusive. Also, if I use any language that hurts you or if I say something that reinforces oppression in some way, please let me know if you can."
If this or something like it had been said at the beginning of the event I went to, I would have interrupted to say that I couldn't make out what people were saying and would have asked that they make room for me at the front so I could hear more and watch faces to help me parse what people were saying. My experience would have been completely different. But without being invited to interrupt, I know that even though they may very well have accommodated me, many people would have had a negative and even angry reaction to me asking for that and thus implying that they were inconsiderate and that my needs were more important than maintaining the flow of their event.
I'll of course continue self-educating and hope to be able to predict most access needs and be ready, but I know I can't predict everything, so it's important that people feel welcomed to tell me in the moment.