These are common deburring tools, but cheaply made. The little button is a part which holds and releases the deburring bit itself. It should really be made of metal, but it's made of plastic, so the surface which rides on the bit wears out and ceases to hold the bit pretty quickly. 

It is a bit difficult to replace. A flat screwdriver can push the button in and pop it downward, then you can push the whole assembly down into the tool. It is simple to remove the button and replace it. The piece is symmetrical top to bottom. The groove fits onto the metal spring. 

Reinserting the assembly is a little more difficult. You need a long, thin tool to push and possibly readjust the assembly around, and possibly the flat screwdriver to engage the button and twist it back the last bit into the opening.

I printed it in PETG. No supports needed. I assume it'll wear out as well, but then I print another.