After installing the Oura app on your mobile device, you'll be asked to create an Oura account.
Creating an Oura account helps to ensure that your data is safe. The app backs up your data automatically from time to time to Oura Cloud. When you switch to a new device using the same operating system (iOS or Android), the Oura app downloads your ring data from your Oura Cloud account to the new device.
Your Oura account is personal, and only one ring can be connected to it at a time. If you want to set up a new ring, follow these instructions: How to set up a new ring
You can check your existing Oura account email from the Oura app settings. To reset your password, follow these instructions: How to reset Oura account password