Descendo is a spell that likely causes any targeted object to move downwards.
Causes something to desend or lower itself
In 1997, Ron Weasley used this spell to lower the ceiling hatch and ladder leading to the Burrow's attic. In 1998, it was used by Vincent Crabbe, who cast this spell on a fifty-foot high pile of junk in the Room of Requirement in an attempt to make it fall over onto Ron.
Descendo is Latin for "I descend".