How to factory reset old phone without affecting iCloud or new iPhone

I just got a new iPhone 11, upgrade from iPhone 8. I transferred everything over to my new iPhone 11 including a recent iCloud backup. I am wondering what should I do to factory reset my iPhone 8? Will it affect my iCloud or iPhone 11? Will it erase anything from this new iPhone 11? Or is it all safe that I have now done a iCloud backup and have transferred everything from the old iPhone 8 to the new iPhone 11?