How to help someone who can't hear in background noise
First understand the problem
Do you want to help someone who complains that conversations going on at the same time interfere with each other, so that they can't really understand what is being said? Or that background noise is exhausting? Or that they can't be sure of the direction of a sound?
Before trying to help someone who suffers this way, you need to understand the cause. Almost always it is due to unbalanced hearing. So first read the page about unbalanced hearing.
Simple ways to help someone who can't cope with background noise or conversations going on at the same time
When talking in a group where you know that there is someone intolerant of background noise, never open a new conversation while another is going on. Also do whatever you can to stop anyone else from opening a new conversation while another is going on. It never ceases to amaze me how often people talk across one another. Even when I have made sure that a group will not be of more than four people before agreeing to be part of it, and even after saying at the outset, "I'm sorry, I can't cope with more than one conversation at a time", some people just can't keep quiet and listen. Even when I remind them, they just say, "Sorry, I forgot", but then do exactly the same thing a few minutes later. I have no alternative but to opt out of attempting to interact with them in the future, which is a pity.
Realise how difficult social situations can be for anyone with unbalanced hearing and do not put pressure on them to attend if they really don't want to. It can do much more harm than good for them to "get out and meet people" when the result is exhaustion and a lowering of self-esteem. The lowered self-esteem can be very real indeed and last for a considerable time.
As some people with unbalanced hearing are embarrassed about it, you can also help by reading about how they can help themselves, and possibly taking some of the tasks off them and onto yourself.
Also realise that anyone with unbalanced hearing is necessarily deaf to some extent in one or both ears. So also read the page on how to be supportive to a deaf person.
More on problems with background noise
Disclaimer: The information on this site is for a lay audience and I cannot be responsible for errors or omissions. The views, strategies, advice and suggestions etc are based on my personal experience and are not necessarily appropriate for anyone else. They should, hopefully, stimulate individuals to develop their own strategies.