Sorry to hear that you've lost access to your account! There are two ways to re-gain access to an account.
Another RememBear device:
If you have another device with RememBear already logged in, you can use this to re-gain access. From the other device locate the 'Add new device' option and follow the instructions. Note, you'll still need to remember your Master Password to get access this way.
Backup Kit:
If you've forgotten your Master Password then you'll need to refer to your Backup Kit. When you initially created your RememBear account you would have been prompted to create a Backup Kit. Hopefully you printed and stored this away securely as recommended! A complete Backup Kit consists of your account email address, New Device Key, and Master Password. You’ll need all of this information to re-gain access to your RememBear account. Unlike many services, RememBear's high level of security means that resetting this information if you lose it is not possible. You can read more about the Backup Kit here.
If you do have access to a complete Backup Kit then simply open the RememBear app on your device. At the login screen, select the “I already have a RememBear account” prompt and follow the instructions.
If you’ve forgotten you Master Password and also lost your Backup Kit, unfortunately there is no way to recover the account or the items stored within it. Your only option at this point is to delete your account. For more info on how to delete your account, click here.