itchy ear, how do i help her?

My dog’s ear has been itching for a couple of days and the only times she’s not itching is when she’s sleeping really. I want to help her but I’m not really sure what’s wrong or how to help. We went to a vet kinda a long time ago and they put this slimy stuff on both her ears I don’t remember what it was, but it was supposed to help fix what was wrong with her ears and currently has only fixed 1 of her ears. I tried to clean it with a cotton ball but she cries whenever I do and I don’t want to hurt her. Is this something I can help her on my own or would we need to go to the vet again?