They will arrange for you to see the diabetic nurse who will go through everything you need to know about GD and diet and if you need insulin then they will go through that with you. You will have regular growth scans and blood tests to check on how bug baby is getting and how well controlled your sugars are.
Your baby will also be delivered early, they only let you go until 38 weeks max, so if your sugars are well controlled and baby isn't looking too big and the placenta is functioning the way it should you will probably be induced at 38 weeks. They sometimes do it earlier if you're not well controlled or baby is too big/not happy in there, but I wouldn't worry about that for now.
It is unusual to develop it after 28 weeks though so you could just have a big baby, good luck