I recently had an additional paper placed under review for peer-reviewed publication. I simply emailed the graduate admissions coordinator for the department with an email explaining the update. I attached a more formal letter to the committee stating the update (in my case, paper title, journal, etc) and also attached an updated version of my CV.
All of the individuals who I emailed were prompt in response and were able to add the updated information to my application package. It was very simple and none of the admissions coordinators seemed to mind.
I hope this helps.
oncearunner got a reaction from pbcup in PhD applicants: Fall 2018