If in a bucket, you can: Stir the mead (must) with a sanitary spoon (gently) and pick up a little speed. But don't whip or froth it like you would when you're trying to aerate it at the start of fermentation. Just gently stir the liquid without disturbing the yeast at the bottom as much as possible and it should release the still suspended CO2 in it. If you stir too vigorously you could get an eruption! So be careful.
EDITED! Oops, it's in a carboy. You could try swirling it I guess, Or I might try the straight end of a racking cane. Not sure how the experts would do it....