Keyboard input
Jump with Spacebar, then press it again while airborne. Kenney clarified this in a reply to a player who had already unlocked float. The official control list maps Spacebar to the controller B button.
If the extra jump does not happen
Check that you have unlocked the ability and review the selected outfit using I. Do not confuse the displayed controller B prompt with the B key. This page does not claim a verified unlock quest chain or a maximum flight distance.
Why the old route is absent
The earlier guide attached exact quest rewards and dependencies without adequate evidence. Those claims were removed; use T to inspect your own in-game task list rather than following an invented prerequisite order.