There are a few ways to fix a dress that is too low cut. One way is to simply wear a tank top or camisole underneath the dress. This will provide more coverage and prevent the dress from being too revealing. Another way to fix a low cut dress is to sew in some fabric to raise the neckline. This is a more permanent solution and will require some sewing skills. If you don't feel comfortable sewing, you can always take the dress to a tailor or seamstress and have them do it for you.