Hi there,
It's exciting to learn that you're using QuickBooks to help manage your expenses and income. Rest assured, I'll be happy to share more info and steer you in the right direction so you can continue to enjoy the benefits offered in the program.
Before handling transactions from a closed period, it's best to get in touch with your accountant to ensure accuracy. Otherwise, QuickBooks provides the flexibility that allows you to manage your transactions with ease. If a transaction change affects your books, QuickBooks will display a pop-up informing you about the impact. I encourage you to check out the following helpful article that shows you how to: Reclassify or move multiple transactions at once.
Let me know if this info helps. Otherwise, you're more than welcome to ask other questions in the comment below.