You can enlarge it slightly with a twist drill. Fit one of the smaller drone reeds into one of the tenor drones. Put the reed in your mouth with the reed tongue free to move. If the reed doesn't sound, bend it away from the body of the reed and hold it for a bit until it stays slightly open. But it's brittle, so be careful.
Some pipers use a head hair jammed at the fixed end of the tongue.
When the drone plays properly, replace it in its stock. Repeat this procedure with the other tenor drone. Repeat for the bass drone, which sounds one octave below the tenor drones. Put the bag under your left elbow and the drones over your left shoulder. Support the bag with your left hand but don't squeeze it.