By default 365 Command users are loaded once every 24 hours. If you recently added users and want to perform actions in 365 Command against them, you can manually force an update to get the new users. You can choose between several options depending on what you want to refresh.
On the screen Account Management -> Data Load Status there are two buttons: "Retrieve New Users and Groups" and "Retrieve Recent Data"
Retrieve New Users and Groups will attempt to sync any new users, groups or mailboxes that have been created since the last sync. This is the fastest option.
Retrieve Recent Data will attempt to sync any user, group or mailbox that has been created OR modified since the last sync. This is the second fastest option.
Additionally, you can also force a refresh of any of the individual data loaders by clicking the 2 arrows that look like a circle next to the individual test.