Assuming he has his own username and workspace, he just needs to go into Perforce and sync to head revision for the entire depot (or individual changelist).
Normally I just use Unreal Engine 4 built-in source control for checking out files, and I do all syncing / submitting / reverts through Perforce app with the editor closed to avoid any unintended breakage or changes.
More info on Perforce: https://www.perforce.com/support/tutorial-video-library/video/basic-operations-p4v
More info on Unreal Engine 4 Source Control: Using Perforce as Source Control | Unreal Engine Documentation