How do I change a Quad to a SubD?

Note: This is my model “broken down”. All of it will be scrapped. But the curved piece in the middle, and the “pieces” to the left, (and far away from the model) which represent “feathers” are done in Quads. Now I need to convert them to SubD.

I actually need step-by-step instructions, because I need to convert them in another model, and use SubD to make them have volume. However, I need to set strict lines along the borders of the “feathers”.

So, I need two ways, if you can do it on this model/then explain to me how you did it, so I can do it on another model, which counts.

• Extension Warehouse : ThomThoms SubD Extension

Really. I don’t know because I’ve forgotten because I’ve had a stroke. Now, I’ve got to look up some unfamiliar terms, because the stroke was on the left side. I know there is a way to do it, I’ve just forgotten how.