What kind of extractor is it? The charcoal fiter is accessed through the suction vent area of your extractor, This could be removed in one of sevaral ways depending on the style of extractor. Some makes supply a filter ready fitted which would then need to be removed if you were to vent out. Others do not supply the filter and you need to then order it as a spare part direct from the manufacturer by quoting your extractor seril number which is on a sticker inside the extractor housing.Alternatively you could try asking whoever you baught it from to order one for you. once you have gained access inside the casing it is usually obvious and very simple to fit the filter. Circulating is only about 70-75per cent as efficient as venting out and would require replacement about every 6 months, so the latter would be my first choice