The handle keeps coming off the hose on my new dryer
Most of the time our various dryer suppliers assemble the hose for us in the factory, so the handle is already connected for you out of the box. If you purchase a dryer where the handle needs to be connected, just twist the hose in to to the handle until it locks in to place. Do not turn the handle itself, just the hose. Most have an arrow on the handle to show you what direction to twist the hose in to attach it (example below).
The 'trick' is to turn the hose anti-clockwise (not clockwise). Keep turning until the hose locks in to place and the handle doesn't come off when pulled. If you turn and turn but nothing happens, and the hose hasn't locked in to the handle, just try the other direction and you're good to go.
Here's one example from the Shernbao model dryers: