The EZ Pen Oiler makes oiling the bobbin case very easy. 
All you need to do is simply pull out the long spout from the bottle, remove the cap and give the bottle a slight squeeze to place a drop of oil in the bobbin case area as directed in your machine user manual. Replace cap, but don’t push the spout back into the bottle as it may contaminate your oil. If the oil becomes cloudy or discoloured replace it. 

Handi Quilter recommends that you oil the bobbin case with every bobbin change.