Helium contracts when it is cold, so once in a warm environment, the helium should expand and the balloon should go back to being fully inflated. That been said please be aware to not put balloons near a fire or hot radiator as the heat can expand the balloon to cause it to pop.
If your balloon doesn’t go back to its normal helium capacity it could mean your balloon is faulty and you should get in contact with us immediately so we can solve the problem.