icloud backup

My sister just got a new phone. When we set it up, we just transferred everything from her old phone to the new one. While that was transferring we realized her last icloud backup was from 2017. Now her new phone only has everything up until 2017. We just backed up her old phone so it’s up to date in the cloud but we weren’t sure how to now transfer it over now that the new phone is at up. I thought maybe if we do the factory reset and then set up the phone again if will have everything but I wasn’t sure if this would delete anything from the icloud. Someone please help as to how we can transfer the old phone over now that the new one is already set up.