If there is a task that you want to do, that is not possible in your waking state, you may find it difficult to accomplish in the dream state.
Even though you are in a realm with no laws, there are still many limitations that are self imposed.
It is your logical side that imposes these restrictions.
The trick is to convince yourself that flight is possible.
Try putting on a jet pack. - These exist in reality, and your mind will have more chance of accepting them.
A hang glider will also produce the desired outcome.
Bit of a stretch, but try putting on an Iron Man suit, and go for a flight test.
Pretend to be a bird, and flap your wings.
Once flight has been accomplished a few times, you should overcome your problem.
Have fun.