In O365 you can only set a user password to never expire using powershell. Here I show you how to do it.
Here are the links I mention in the vid:
Support link:
https://support.office.com/en-us/article/Set-an-individual-user-s-password-to-never-expire-f493e3af-e1d8-4668-9211-230c245a0466?wt.mc_id=o365_portal_mmaven&ui=en-US&rs=en-US&ad=US
Microsoft Online Services Sign-In Assistant:
https://www.microsoft.com/en-us/download/details.aspx?id=41950
Azure Active Directory Connection:
http://connect.microsoft.com/site1164/Downloads/DownloadDetails.aspx?DownloadID=59185