Easy as pie.
Remove fur fixing plate around the battery enclosure. Carefully roll back the fur to reveal the speaker housing.
Using a long thin object, carefully push into the upper holes and prod the speaker membrane. A t some point you will hear the Furby's voice. Keep a note of that hole then take a cotton bud (q-tip) and cut the buds off. Now using that straw push into the hole that you identified. Snip bud and super glue in place. Result.