How to give credit for conference presentations on CV?
All official and known conferences will need the authors to present their accepted work in oral or poster manner, and will publish the proceedings of the conference. I am not sure what you mean by undergraduate conference. But a presentation, where no paper has been presented to the research community, is not a big shot to be declared in CV, at least because there is no clear evidence for such accomplishment. 

If there were any paper, You would mention the paper in a typical manner in your CV (considering yourself and any other one, who had any contribution) and insert an unpublished assertion in front of it. But in this situation, the better idea could be citing the thing in your CV, as a Given Presentation at blah blah blah Conference. If you do it, you might better explain something about undergraduate conference, because the reader may not be aware of this term, leading to confusion.

Good luck