Get your manager involved, get a new job for yourself, or learn to live with it. Maybe start sending job posts to this other person and see if you can help get

Get your manager involved, get a new job for yourself, or learn to live with it. Maybe start sending job posts to this other person and see if you can help get them a new job? It’s very unlikely that you’ll be able to help this other person “improve” (and it might cause new problems for you if you try). You might also need to realize that the other person isn’t underperforming and that you don’t have full information about the situation.