A strapless dress that is too big can be given a dart or additional closure by attaching ribbons in a corcet pattern, as is often seen on the back of Indian dresses.
A good way to fix a strapless dress that is too big is by taking in the sides until it is comfortable. If you sew it from the inside, the changes should not be very, if at all, noticable.
Bring it to a tailor and they will be able to bring in the top for you so that the strapless dress stays up on its own. Or, you could add straps to keep it up if that's the problem.
That is a great idea! How would you go about doing it? Is it easy to do? Thanks add a comment