Navigate to the Calendar section of Outlook Mobile. Tap on the Menu button in the top left-hand corner of the app. From the menu that appears, tap the + button in the top left-hand corner. Tap on Add Shared Calendar on iOS, or Add a shared calendar on Android. Search for a person, room, or other mailbox in your organization. Tap the + button next to the person, room, or other mailbox to add that shared calendar. The newly added shared calendar will appear in the list of calendars under your Microsoft 365 account.