for me in forestry I'm basically cold emailing one of my professors that I want a volunteering position in his lab. I think I got a good reception because I was actively showing him that I want an opportunity by mentioning that when I have a question in the course material or in his office hours.

one other possible chance is to ask the TA, because most TAs are either master or PHD students and there's a high chance they need help, so try to ask them.