Asking for a friend.
If an author is added to a biorxiv paper, but does not want to be part of it, is there any recourse for him/her?
In common with other publishing platforms, bioRxiv requires the submitting author to confirm that all authors have agreed.
An article may be deposited in bioRxiv in draft or final form, provided that it concerns a relevant scientific field, the content is unpublished at the time of submission, and all its authors have consented to its deposition.
Your friend should contact bioRxiv to explain the situation. The contact email listed on the FAQ page is:
biorxiv.feedback [at] cshl.edu
Submitting a manuscript for publication without the consent of all of its authors is serious misconduct. Depending on the specifics of the situation, your friend should complain about this to administration at the relevant institutions.