Hi there. First of all, welcome to MP. It's good to have you here. This is a great place to learn/share your knowledge of growing mj like a pro. It's also filled with members that are more than willing to help you out. I hope to see you around the forums sometime in the future.
First, are they in dirt or hydro? What kind of lighting do you have? Four months of veg is a LOOOONNNGGGG time. How big is the plant? With 4 months of veg, the plant must be HUGE! Did it break completely off or is it still hanging on? Do you have any pictures? I would say just leave it alone and it will either survive or die. If it dies, more tops will sprout in a week or two to replace it. Search around on the search engine provided at this site for topping. Hope this helps. Keep us posted. Take care and be safe.