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Fresh air vents into room

I have an internal garage that has been converted into a room at some stage. Other than a French style door at one end, the room does not have any windows or natural ventilation and therefore is a bit musty. I would like to add some sort of simple ventilation to bring outside air into the room. I don't really know what can be done but even just a simple air vent or two cut through the glass panes in the French door would suffice. Recommendations gladly taken. Thanks