1. A strong will to keep trying - you've done it once, second time is easier!
2. Knowing that the Internet's got your back - there are people like you out there, who have faced and conquered similar problems; find them out, and learn from them!
3. Mix it up - since you'd originally left your field and are returning, you'd have done something else in the interim, right? Use that experience to make your return more fruitful!
I had to relearn calculus because I decided to study stats after finishing my BA in psychology. I was good at Math before but now I have to relearn it.. What did I do???? JUST LEARN IT AGAIN! I listened to lectures online; read the textbook.. I really don't think there is any shortcut to this. Also I am sure you didn't forget everything. You will surely learn faster the second time around.
If I forgot everything then it probably would be easier to learn new programming technologies. On the other hand I might have also forgotten why programming is cool.
1. A strong will to keep trying - you've done it once, second time is easier! 2. Knowing that the Internet's got your back - there are people like you out there, who have faced and conquered similar problems; find them out, and learn from them! 3. Mix it up - since you'd originally left your field and are returning, you'd have done something else in the interim, right? Use that experience to make your return more fruitful!