If you can pull it back part way, you should be able to do this:
Set aside two sessions of five to ten minutes per day in which you can do this exercise. Don't make it hurt, but apply enough tension to feel it. In addition, you probably also need to stretch the frenulum, that little web inside. For that, do this:
This one you can do at the same time you do the first one, and you can also do it several times throughout the day after you pee.
There is really no way to predict how long it may take you, but if you're faithful to doing it every day, my guess is about two months. Once you achieve full retraction, I advise you to continue stretching for an additional month to allow time for skin cells to grow. After that, you should have no more trouble. One habit you may wish to adopt is that of retracting when you pee. That keeps everything in working order.
Please report back on your progress.