If it's just the ring that moves, it may be broken rollers.
If the entire front barrel wiggle up, down and sideways probably loose screws
holding the lens assembly to the mount.
Some zooms are pretty simple to split. Look for three screws around the tube under the zoom ring
If present, when removed; the tube will slip forward. There MAY be three screws around the outside of the exposed tube that have loosened.
Tighten 'em.

If that's not it, MARK the tube and lens mount for correct orientation when reassembling remove the
screws and the lens will split, usually just ahead of the diaphragm housing. If it's this style the screws holding to
mount should be visible.