@Aimthedame
Unfortunately, there is no particular way to refresh/reset the information when it is tied to the Gallery items directly.
However, you can force it to refresh by changing the calendar name. You can change your Items property to the following formula:
Office365Outlook.CalendarGetItems(If(lclUpdateCalendar, "", ddCalName.Selected.Name)).value
Then, at some action - a button OnSelect, a Timer action, anything...you can put the following formula:
UpdateContext({lclUpdateCalendar:true}); UpdateContext({lclUpdateCalendar:false})
This will cause the Item formula to reevaluate and it will force a refresh.
I hope this is helpful for you.