For reaming it with a drill, I'd secure it to a table or other lateral surface gently. Then I'd determine the depth of the moderator before the barrel begins. Then choose a bit somewhat larger than the moderator hole and measure the bit so that it you don't touch the end of the barrel. Then I'd carefully drill the moderator out a bit. Then blow out any shavings and open the breech and blow compressed air to blow out any shavings that might have gone in the barrel.Mounting it in a vertical vice with a drill press would be better, but will be a lot more difficult and shavings will fall into the barrel unless you plug it with cotton or something.
Howdy gunnewb, A simple approach (assuming you have the most basic tools) is to take a flat head screw driver and a *gentle* hammer to separate it. Wrap the flat head with electric, masking, or scotch tape then lightly tap around all edges with a hammer. You should not need a vise. Just position the air rifle on a soft surface and "pin" the stock with your knee. A make and model of the air rifle would help the folks here as someone has probably been in the same boat.After the attachment is off, buy a cheap round file and work your way through the baffles. This will be like cologne or perfume....a little dab will do you.