There is two issues here the iPad’s local storage and what you have on your iCloud account on Apples servers.
Any data that you hadn’t sync’ed up to your iCloud account on your iPad will be lost! Your stuff that is on Apples servers is still safe. You’ll need to log in into your iCloud account from another iOS or macOS device to gain access to it. You will use your Apple ID and the password you setup for it. Apple uses a two-factor authentication [https://support.apple.com/en-us/HT204915|Two-factor authentication for Apple ID] so make sure you can do it.